BEIRUT, Lebanon — The commander of the American-backed militia in Syria said Tuesday that it would attack Turkish forces if they entered northeastern Syria, while Turkey’s president, Recep Tayyip Erdogan, indicated that such an operation was imminent.
“We will resist,” Mazlum Kobani, commander of the Kurdish-led militia, said in an interview with The New York Times. “We have been at war for seven years, so we can continue the war for seven more years.”
Mr. Erdogan, speaking to reporters on a flight to Serbia, said the operation might happen before the news could be printed. Turkish troops were being bused to the Syrian border in preparation for an incursion, Turkish media reported. And the Turkish Defense Ministry said on Twitter that preparations to enter Syria “had been completed.”
The escalating challenge came after President Trump agreed to let the Turkish operation go forward and to move American troops out of the way. On Monday, American troops withdrew from posts near two Syrian towns near the border.
The threat of armed resistance from the militia, a force trained and armed by the United States, raises the risks for Turkey as it weighs sending troops into Syria, and for the United States, which could find itself on the sidelines of a new front in Syria’s war — this time between two of its allies.
There was still confusion among allies and American officials about the administration’s policy as set out in seemingly contradictory statements by Mr. Trump and administration officials, and American officials said Tuesday that some senior Pentagon officials had been blindsided by the decision to pull American forces back from the border.
The Kurdish-led militia, the Syrian Democratic Forces, or S.D.F., partnered with the United States to defeat the Islamic State in Syria. Since then, the militia, with American backing, has retained control of a large swath of northeastern Syria.
Turkey considers the militia part of a Kurdish guerrilla movement that threatens Turkey, and Mr. Erdogan has demanded a 20-mile-deep buffer zone along the border that Turkey would control to keep back any Kurdish forces.
Speaking by telephone from Syria, Mr. Kobani said he had been frustrated by the White House’s announcement on Sunday that the United States would stand aside for a Turkish incursion, and that the lack of clear, predictable policies from Washington had made it hard to plan.
“There should not be any ambiguity,” he said.
He spoke of United States troops who had helped his forces fight the Islamic State as comrades-in-arms and said any rupture in that partnership could destabilize the region.
“We fought with U.S. forces to get rid of terrorism, and we are still in this continuing battle,” he said.
He called on Americans to “put pressure on their political and military leaders to stop the Turkish attack,” which he said would lead to “big massacres.”
Mr. Trump said Sunday that the United States would not block a Turkish advance. But on Monday he said that he would “obliterate” Turkey’s economy if its military did anything “off limits,” without defining what that meant, and his aides insisted that he had not given a green light to an invasion.
On Tuesday, he said that he had invited Mr. Erdogan to visit the White House next month.
Two American officials, speaking on condition of anonymity to discuss private diplomatic and military conversations, said that given the apparently contradictory statements by Mr. Trump, the Turks seemed flummoxed about what support, if any, they might get from the United States. As a result, they may be rethinking what to do next, the officials said.
Still, several American officials said they expected a Turkish incursion to begin Wednesday, even in the face of congressional blowback. Senator Lindsey Graham, Republican of South Carolina, said in a tweet directed at Turkish officials that they “do NOT have a green light” to advance and that “there is massive bipartisan opposition in Congress, which you should see as a red line.”
Turkish news media reported that Turkey’s armed forces were preparing F16 jets and Howitzers. Special forces troops were arriving in buses at the border crossing of Akcakale just across from the Syrian town of Tel Abyad, and cranes were moving into position to lift concrete barriers at the border.
Tel Abyad was one of two towns evacuated by American forces on Monday. The other was Ras al Ain. American officials said Tuesday that Turkey had amassed several hundred troops, including tanks and other armor, near the two towns.
Political analysts with knowledge of the plan worked out with American officials said Turkey planned to set up four bases or combat posts in a narrow area along the border, and had agreed to stick to a limited action as a first stage.
“I would expect Turkey to implement a graduated incursion, then go back to negotiation with the U.S. from a stronger position,” said Ozgur Unluhisarcikli, Ankara director of the German Marshall Fund of the United States. “Then when it is in a better situation, do a second operation, and a third. That is a graduated strategy.”
Mr. Trump’s argument that pulling United States forces from Syria was a fulfillment of his vow to get Americans out of “endless wars” unleashed a wave of criticism, much of it from Republican lawmakers. Many argued that withdrawing the roughly 1,000 United States troops in northeastern Syrian would open a void that could be exploited by President Bashar al-Assad of Syria or his Russian and Iranian allies, or by the Islamic State.
Mr. Trump has not ordered a full withdrawal from Syria. The order on Sunday was only to relocate roughly 100 to 150 troops that had been stationed near the Turkish border. About two dozen were pulled back on Monday.
But analysts feared that any redeployment of Kurdish troops to fight Turkey in the north would take them away from the battle against the Islamic State. The Islamic State was driven from its last territory in Syria in February, but the S.D.F., with the support of American Special Operations Forces, continue to battle the group’s remnants.
The American officials said the S.D.F. was already beginning to move off some of its counterterrorism missions against the Islamic State.
“The danger of ISIS is real,” Mr. Kobani said, adding that it maintains sleeper cells throughout the territory. His forces also oversee prisons and camps holding tens of thousands of former Islamic State fighters and their families, which Mr. Trump has said Turkey could take over.
Mr. Kobani said there had been no conversations with the United States about handing over these prisoners to Turkey and he called the idea “impossible.”
Mr. Kobani said that he would prefer that the United States remain in Syria until the Islamic State and its remnants are destroyed and the country reached a “complete political solution that guarantees everyone’s rights.”
The Pentagon on Tuesday challenged published accounts asserting that Mr. Trump’s decision to order American troops to pull back from the border surprised many Defense and State Department officials.
Defense Secretary Mark Esper and Gen. Mark Milley, the new chairman of the Joint Chiefs of Staff, “were consulted over the last several days by the president regarding the situation and efforts to protect U.S. forces in northern Syria in the face of military action by Turkey,” said Jonathan Hoffman, a Pentagon spokesman.
Several Pentagon officials confirmed that there had been discussions about Mr. Erdogan’s threats to invade northern Syria, but said that they had no hint that Mr. Trump was going to order American troops to step aside and leave their Syrian Kurdish allies vulnerable to attack.
In fact, the officials said, both Mr. Esper and General Milley warned their Turkish counterparts last week that any such cross-border operation would seriously damage United States-Turkish relations.
American commanders had expected to have some advance notice before Turkey launched an operation in northern Syria, and said they would probably have pulled back American forces to avoid advancing Turkish troops.
But until Mr. Trump’s order on Sunday, there were no plans to pull back pre-emptively, the officials said.
In a tweet on Tuesday, Mr. Trump insisted that he was not betraying the Kurds.
“We may be in the process of leaving Syria, but in no way have we Abandoned the Kurds, who are special people and wonderful fighters,” he said.
He warned that “any unforced or unnecessary fighting by Turkey will be devastating to their economy and to their very fragile currency.”
Mr. Kobani says he would prefer to stick with the United States and work for a stable Syria, but that his forces are ready to attack if Turkey invaded.
“There will be lots of resistance if they cross the border,” he said. “We will not accept them on our land in any way.”