Mr. Bolton will meet on Tuesday with President Recep Tayyip Erdogan of Turkey, who argued to Mr. Trump in a phone call last month that the Islamic State had been defeated, and that American troops were therefore no longer needed to aid Kurdish fighters. Turkey considers the Kurdish forces a terrorist body bent on carving out a separate nation.
Before the Turkey visit, Mr. Bolton was expected to meet with Prime Minister Benjamin Netanyahu of Israel over dinner on Sunday evening. Mr. Netanyahu has also been concerned about the American plan, for fear it will leave a vacuum and embolden Iran.
In Jerusalem, Mr. Bolton described the conditions as “policy decisions that we need to implement,” and he said a timeline for a withdrawal would be necessary only once those stipulations were met. He said that Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, would negotiate with Turkish officials this week over the protection of the Kurdish fighters.
Mr. Bolton’s comments seemed to expand on a classified memo he wrote to cabinet officials on Dec. 24 that outlined a strategy for Turkish troops to replace the roughly 2,000 American troops conducting counterterrorism operations against the Islamic State in northeastern Syria, according to two Defense Department officials.
Mr. Bolton’s memo came after Mr. Trump and Mr. Erdogan spoke by phone on Dec. 23. After that conversation, Mr. Trump tweeted: “I just had a long and productive call with President @RT_Erdogan of Turkey. We discussed ISIS, our mutual involvement in Syria, & the slow & highly coordinated pullout of U.S. troops from the area. After many years they are coming home.”
Mr. Bolton also wrote in the memo, which was first reported by The Wall Street Journal, that the administration’s objectives in Syria remained consistent. Those goals have included routing the Islamic State from its last enclaves in the Middle Euphrates River Valley, ousting Iranian-commanded forces and pursuing a diplomatic resolution to the country’s civil war.
Pentagon officials almost immediately expressed skepticism that the Turkish military, which has struggled to carry out limited operations along its border with Syria in the past two years, could execute expansive counterterrorism operations deeper into Syria, toward the border with Iraq. Moreover, American military planners said any Turkish movements into northeastern Syria would lead to clashes with the Syrian Kurdish-Arab coalition known as the Syrian Democratic Forces, or S.D.F.