(Updates with more comments from the U.S. official, background)
By Humeyra Pamuk
WASHINGTON, Oct 15 (Reuters) - The United States will mount diplomatic pressure on Turkey and threaten Ankara with more sanctions to persuade it to reach a ceasefire and halt its military offensive in northeastern Syria, a senior administration official said on Tuesday.
A week after reversing U.S. policy and moving troops out of the way to allow Turkey to attack Washington's Syrian Kurdish allies, President Donald Trump announced a package of sanctions to punish Ankara but Turkey ignored the penalties and pressed on with its assault on Tuesday.
Speaking at a briefing, the U.S. official said Turkey's incursion has caused 'a mess' in what he said once was a relatively stable part of northern Syria and that Washington was ratcheting up the pressure for it to stop.
"The plan is to continue the pressure on Turkey as we evaluate our chances to return the relationship to normal, a major element of that return to normal would be a ceasefire," the senior administration official said.
"And by ceasefire what I mean is forces on the ground stop moving on the ground. Certainly Turkish forces and I think we could probably speak for the SDF," he said, referring to Washington's former Kurdish allies.
The United States announced on Sunday it was withdrawing its entire force of 1,000 troops from northern Syria. The SDF immediately forged a new alliance with President Bashar al-Assad's Russia-backed government, inviting the army into towns across the breadth of its territory.
U.S. Vice President Mike Pence on Monday said he would be leading a delegation to Turkey for talks. The official did not provide any details about the planned the visit but said if Ankara did not respond to diplomatic efforts, there could be more sanctions.
"We're planning to increase sanctions and other measures many of which have been signaled to the administration, absent a resolution to this crisis," the official said. (Reporting by Humeyra Pamuk and David Brunnstrom; Additional reporting by Lisa Lambert and Susan Heavey Editing by Alistair Bell)