The Biden administration and U.S. military leaders are increasingly concerned about rising tensions with Iran, and they are looking at the New Year as a potential flashpoint, according to two defense officials and two administration officials familiar with the matter.
The growing confrontation with Iran has prompted a debate inside the administration about how to respond to attacks and provocative acts by Iran and its proxies in the region, current and former U.S. officials said.
Tensions ratcheted up after the Oct. 20 attack on the U.S. military base known as At Tanf Garrison in southern Syria, when five suicide drones packed with explosives and shrapnel were launched at the base. No U.S. troops were killed in the assault, but several structures on the base were badly damaged.
Three U.S. defense officials and two administration officials say Iran was behind the attack and launched it through proxy forces with the intent to kill American troops. In an interview with Time Magazine, the commander of U.S. Central Command, Gen. Frank McKenzie, did not blame Iran for the attack, but he did say whoever conducted it "was clearly trying to kill Americans."
Iran launched the attack in retaliation for an Israeli strike in Syria that killed and wounded several Iranian citizens, the U.S. officials said. The Israeli strike targeted a shipment of advanced missile parts intended for Iranian-backed groups operating in Syria.
The U.S. military had advance warning that the drones were inbound, and they were able to move most of the 200 U.S. soldiers away from the base to avoid any casualties, according to the five officials.
The Biden administration called for options to respond.
Within hours of the attack, McKenzie briefed Secretary of Defense Lloyd Austin on options to retaliate against Iran. The options were largely kinetic, the five officials said, including airstrikes against targets inside Iran that could lead to the death of Iranians. But senior Biden administration officials worried that killing Iranians would escalate the situation and asked for more options.
CENTCOM came back with a second round of options that included airstrikes and cyber possibilities, which Austin and Chairman of the Joint Chiefs Gen. Mark Milley briefed to the White House. Ultimately the interagency decided to respond with diplomacy, sending a message to Iran rather than delivering airstrikes or a cyberattack, according to one of the defense officials and one of the administration officials familiar with the response.
"The interagency reviewed more options available to send Iran to make clear to Iranians how seriously we would take any future lethal strikes," according to the administration official.
Despite the U.S. message to Iran, the at Tanf base was threatened again this week, when two drones breached the immediate area around the garrison. A British fighter jet fired an air-to-air missile to shoot down one drone, while the other flew away. Defense officials are not certain whether this was an attempted attack that was thwarted or if the drones were probing the U.S. defenses. Either way, it only intensified concerns about threats to Americans escalating in the coming weeks, according to two U.S. military officials.
The attack on at Tanf and other incidents, including a drone assault on a commercial oil tanker, the MT Mercer Street, in August off the coast of Oman that the U.S. and Britain blamed on Iran, has sparked a debate in and outside the administration about how to deter Iran without igniting an all-out war, with some senior military officers favoring a tougher line, according to two current and one former U.S. official with knowledge of the discussions.
Asked for comment, the White House referred NBC news back to a conference call it conducted last week, when a senior administration official said that after months of attacks by Iran against Americans in Iraq under the Trump, the Biden administration "used a combination of deterrence, including two rounds of airstrikes, and also a lot of diplomacy to both deter and also de-escalate some of these tensions."
"So, since July, we've had about five months of calm - so, the longest period of calm we've had in Iraq, I think, really in three years. And we're looking for that to continue," the official said. "But we very much anticipate, heading into the first part of next year, there's the anniversary of the Soleimani strike, there's Iraq's government formation process, and a few other milestones, that some of these attacks might start up again. But we'll be very ready for that and prepared."
One of the main reasons U.S. officials believe Iran and Iranian-backed groups will increase attacks against U.S. troops in Iraq and Syria around the New Year is the U.S. military is scheduled to officially end its combat mission in Iraq on Dec. 31, according to an agreement between the U.S. and Iraq.
On Dec. 9, the Iraqi government announced American troops had ended their combat mission. In reality, U.S. troops in Iraq transitioned to a training mission in July 2020, and thousands of U.S. troops will remain in both Iraq and Syria in this advisory role into 2022, but announcement was meant to ease pressure on the Iraqi government by Iranian-backed groups, according to two defense officials and two U.S. military officials.
Earlier this month, Iranian Quds Force Commander Sardar Qaani warned Americans that they will take action against American troops still in the region after the deadline.
"After January 1st, all bets are off," one U.S. defense official said.
U.S. officials are also watching the Jan. 3 second anniversary of the U.S. assassination of Iranian Quds Force Leader Gen. Qasem Soleimani as another possible flashpoint.
"We are aware of potential threats that could increase in the coming weeks and we are making sure we are going to be ready for them," an administration official said.
Michael Knights of the Washington Institute for Near East Policy, who tracks Iranian-backed militia activity, said he expects the militias to mark the upcoming anniversary of Soleimani's death and the new year when they believe U.S. troops should be completely withdrawn from the country. But he said it's unclear how far they will go.
The drone flight last week over at Tanf and drone flights this month in Erbil in northern Iraq where U.S. forces are located suggest the militias are probing U.S. defenses at military outposts, according to Knights.
The track record of the militias over the past year "shows they're quite cautious" and have tried to avoid killing U.S. troops or personnel, as that would likely trigger a U.S. military response, Knights said.
"My gut feeling is they are going to try to do non-lethal things - to do the minimum to placate the support base," he added.
For the United States and its allies, the question over how best to respond to Iran and its proxies is closely tied to efforts to prevent Tehran from acquiring nuclear weapons through diplomacy and economic pressure.
Some U.S. officials worry that retaliating to every Iranian provocative action could prove counterproductive and derail talks between Iran and world powers aimed at reviving a 2015 nuclear agreement. But others, including some prominent former officials who served in the Obama administration and former Democratic lawmakers, argue that only the threat of military force will ensure diplomacy succeeds.
"Without convincing Iran it will suffer severe consequences if it stays on its current path, there is little reason to hope for the success of diplomacy," said a statement released Friday by former Defense Secretary and CIA director Leon Panetta, former undersecretary of defense Michele Flournoy, former Democratic lawmakers Jane Harman and Howard Berman, retired Gen. David Petraeus, former senior diplomat Dennis Ross and commentator Robert Satloff.
The group called for high-profile military exercises and for responding to attacks by Iran or its proxies, citing the October attack on the at Tanf base.
"There's a need for them to see that we will respond to some of these attacks," said Dennis Ross, who crafted Middle East policy under several presidents. Iran's "readiness to do these things shows a loss of fear," he said.
The 2015 nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA), eased sanctions on Iran in return for strict limits on its nuclear activities. But President Donald Trump pulled the U.S. out of the agreement in 2018 and reimposed sanctions. Iran has since breached the restrictions on its nuclear program, enriching uranium up to 60 percent purity, employing advanced centrifuges and hampering the work of U.N. inspectors.
Talks in Vienna on the nuclear accord have stalled since the election of a hardline cleric, Ebrahim Raisi, as Iran's president in June. On Friday, Iran and the other parties finally agreed to an agenda for the discussions, but U.S. and European officials struck a pessimistic tone.
"So we made some progress, not enough certainly at a pace that will not be sufficient to get to where we need to go before Iran's nuclear advances render the JCPOA a corpse that cannot be revived," a senior State Department official told reporters Friday.
"There is a diplomatic path, it is a preferred path," the State Department official said. "If it's not chosen, then unfortunately, we will have to look at other tools to ensure that the president's goal, his commitment, which is that Iran will not acquire nuclear weapon, is realized."
Another administration official said the Biden administration is not going to allow a nuclear Iran on their watch and will have to act soon.
"The options are closing down and people are starting to see that," the administration official said.
The U.S. still has about 2,500 troops in Iraq and 900 in Syria. While some equipment and capabilities have shifted in recent weeks, there are no plans to change the footprint in either country, according to U.S. military officials. The U.S. still has defensive capabilities in place, the officials stressed.
Experts and former U.S. officials say it could be only a matter of months before Iran reaches the stage where it becomes a nuclear threshold state, with the technical ability to quickly build nuclear weapons if it chose to.
The State Department did not immediately respond to requests for comment.
Iran's mission to the United Nations did not comment directly on the At Tanf incident but said U.S. troops stationed in Syria were violating that country's sovereignty.
"The position of the Islamic Republic of Iran on its presence in Syria has always been abundantly clear. Iran is in Syria at the invitation of the legitimate, UN-recognized government of the Syrian Arab Republic and plays an advisory role there. It is, in fact, the United States - as the violator of Syrian sovereignty - that should be aware that itself has direct responsibility for any such trespass," Iran's U.N. mission said in an email to NBC News.
The Israeli government worries that Iran could soon conceal aspects of its nuclear work in a way that would make it impossible for the outside world to verify if it had nuclear weapons or be on the verge of a nuclear capability, said Jacob Nagel, who served as acting national security adviser to former Israeli Prime Minister Benjamin Netanyahu.
"We are getting down to the decision point," Nagel said.
Israel's embassy in Washington declined to comment.
Mossad chief David Barnea said earlier this month that Israel will do "whatever it takes" to ensure Iran never builds a nuclear weapon.
During a visit to the U.S. last week, Israeli Defense Minister Benny Gantz said that he informed U.S. officials that he had ordered the Israeli military to prepare for a potential strike against Iran.