By Steve Holland
WASHINGTON (Reuters) - U.S. President Donald Trump struck a blow against the 2015 Iran nuclear agreement on Friday in defiance of other world powers, choosing not to certify that Tehran is complying with the deal and warning he might ultimately terminate it.
Trump announced the major shift in U.S. policy in a speech in which he detailed a more confrontational approach to Iran over its nuclear and ballistic missile programs and its support for extremist groups in the Middle East.
Trump accused Iran of "not living up to the spirit" of the nuclear agreement and said his goal is to ensure Tehran never obtains a nuclear weapon. He suggested Iran might be working with North Korea on its weapons programs, an accusation that has not been substantiated.
"We will not continue down a path whose predictable conclusion is more violence more terror and the very real threat of Iran's nuclear breakout," Trump said.
While Trump did not pull the United States out of the agreement, aimed at preventing Iran from developing a nuclear bomb, he gave the U.S. Congress 60 days to decide whether to reimpose economic sanctions on Tehran that were lifted under the pact.
That increases tension with Iran as well as putting Washington at odds with other signatories of the accord such as Britain, France, Germany, Russia, China and the European Union.
If Congress reimposes the sanctions, the United States would in effect be in violation of the terms of the nuclear deal and it would likely fall apart. If lawmakers do nothing, the deal remains in place.
Trump warned that if "we are not able to reach a solution working with Congress and our allies, then the agreement will be terminated."
Trump's harder line on Iran was likely to infuriate Tehran but was welcomed by Israel.
Israel's intelligence minister described Trump's speech as "very significant" and one that could lead to war given threats that preceded it from Tehran.
The move was part of Trump's "America First" approach to international agreements which has led him to withdraw the United States from the Paris climate accord and the Trans-Pacific Partnership trade talks.
Trump on Friday also gave the U.S. Treasury Department broad authority to impose economic sanctions against people in the Islamic Revolutionary Guards Corps or entities owned by it in response to what Washington calls its efforts to destabilize and undermine Iran's opponents in the Middle East.
"We hope that these new measures directed at the Iranian dictatorship will compel the government to re-evaluate its pursuit of terror at the expense of its people," he said.
U.S. Secretary of State Rex Tillerson acknowledged the latest strategy of coaxing Congress to act may not work.
"What we are laying out here is this is the pathway we think provides us the best platform from which to attempt to fix this deal," he said. "We may be unsuccessful. We may not be able to fix it. And if we're not then we may end up out of the deal."
The Republican president has been under strong pressure from European leaders and U.S. lawmakers to swallow his concerns and certify the nuclear deal because international inspectors say Iran is in compliance with it.
European allies, some of which benefit economically from a relaxation of sanctions on Iran, have warned of a split with the United States over the nuclear agreement and say that putting the deal in limbo as Trump has done undermines U.S. credibility abroad.
International inspectors say Tehran is in compliance with the nuclear accord, under which crippling economic sanctions on Iran were lifted in exchange for it agreeing to drastic limits on its nuclear program. Iran always denied allegations that it aimed to build a nuclear bomb.
(Reporting by Steve Holland; Additional reporting by Makini Brice, Patricia Zengerle, Jonathan Landay, Justin Mitchell, Tim Ahmann and Arshad Mohammed in Washington, Andrea Shalal in Berlin, Dmitry Solovyov in Moscow, Parisa Hafezi in Ankara and Dan Williams in Jerusalem; Editing by Yara Bayoumy and Alistair Bell)