U.S. senators who have criticized Trump for failing to halt the Turkish assault, said they would press ahead with legislation to place sanctions on Turkey despite the ceasefire announcement.
Turkey agreed on Thursday to pause its five-day offensive on Syria to let Kurdish forces withdraw from a "safe zone" that Ankara had sought to capture in a deal hailed by the Trump administration and Turkey as a complete victory.
The truce was announced by United States Vice President Mike Pence after talks in Ankara with Turkey's President Tayyip Erdogan.
If implemented, it would achieve all the main objectives Turkey announced when it launched the assault eight days ago: control of a strip along the Syrian more than 30 km deep, with the Kurdish YPG militia, formerly a close U.S. ally, obliged to pull out.
"The safe zone will be primarily enforced by the Turkish Armed Forces," read a joint U.S.-Turkish statement released after the Thursday talks.
A Turkish official told Reuters that they got "exactly what we wanted" from the talks, while Turkish Foreign Minister Mevlut Cavusoglu described the measure as a pause to allow the Kurdish fighters to withdraw.
Kurdish fighters would be forced to give up their heavy weapons and their positions would be destroyed, Cavusoglu said. He declined to call the agreement a "ceasefire", saying ceasefires could be agreed upon only by legitimate sides, and not by a Kurdish militia that Turkey considers a terrorist group.
"When the terrorist elements completely leave the safe zone, we can stop the operation," Cavusoglu said.
The joint declaration said Washington and Ankara would cooperate on handling Islamic State (IS) fighters and family members held in prisons and camps, a major international concern.
Pence said Washington had already been in contact with the Kurdish-led Syrian Democratic Forces (SDF), which had agreed to withdraw and were already pulling out. However, the Kurdish position was not clear.
Aldar Xelil, a leading Syrian Kurdish politician, said the Kurds would soon issue a statement. He said the Kurds had rejected the Turkish safe zone in the past. They would abide by the ceasefire but would defend themselves, Xelil said on Al Arabiya television.
Pence said that once the pause became permanent, Washington would go ahead with its own plans to withdraw its entire military force from northern Syria, which had partnered with the Kurds to fight against IS.
The deal struck with Erdogan also provided for Turkey not to engage in military operations in the flashpoint Syrian border town of Kobani, Pence said. However, Cavusoglu said Turkey had given no committments to the effect.
The Turkish assault has created a new humanitarian crisis in Syria with 200,000 civilians taking flight, a security alert over thousands of IS fighters potentially abandoned in Kurdish jails, and political backlash at home for Trump.
The U.S. head of state has been accused of abandoning Kurdish-led fighters in Syria, Washington's main partners in the battle to dismantle the IS self-declared caliphate in the country, by withdrawing troops from the border just as Ankara launched its offensive on Oct. 9.
The U.S. House of Representatives had condemned the president's policy on Wednesday in a vote for sanctions backed by Democrats as well as a majority of his fellow Republicans.
The Turkish assault began after Trump moved U.S. troops out of the way following a phone call with Erdogan. Trump announced sanctions on Turkey following the launch of the assault, but his opponents said these were too mild to have an impact. Pence said the sanctions would now be lifted once the ceasefire became permanent.
However, U.S. Republican Senator Lindsey Graham and Democratic Senator Chris Van Hollen intended to proceed "full steam ahead" with proposed legislation to impose tougher sanctions, a spokeswoman for Van Hollen said.
If successful, the Thursday deal could smooth over a major rift between Washington and Turkey, its main Muslim ally in NATO.
Meanwhile, the Kurds responded to the announcement of the U.S. withdrawal by effectively switching allegiances and have already invited forces of the Syrian government, backed by Moscow and Tehran, into towns and cities in areas they control.