By David Gauthier-Villars in Istanbul, Vivian Salama in Washington and Dion Nissenbaum in Beirut 

ISTANBUL -- Turkey dismissed a U.S. call for an immediate cease-fire in northeast Syria, pressing ahead with its military offensive as senior Trump administration officials rushed to Ankara to try to halt fighting triggered by the withdrawal of American troops from the region.

President Trump on Tuesday dispatched Secretary of State Mike Pompeo and Vice President Mike Pence to the Turkish capital, where they will meet with President Recep Tayyip Erdogan on Thursday to urge him to stop a weeklong military incursion in northeastern Syria.

But Mr. Trump, defending his decision to withdraw U.S. troops from northeastern Syria, refrained on Wednesday from criticizing Turkey for the assault on Kurdish-held areas, saying Ankara's incursion has "nothing to do with us."

The U.S. imposed sanctions and raised steel tariffs on Turkey after the incursion, and congressional leaders were moving on Wednesday toward adopting a measure harshly critical of the U.S. withdrawal, in large part because it meant abandoning a crucial ally, the Kurds. But Mr. Trump during a meeting with his Italian counterpart dismissed the criticism, saying the Kurds -- a group with which Washington had allied to fight Islamic State -- are "not angels."

The Turkish military operation and subsequent withdrawal of U.S. troops prompted Kurdish fighters to seek help from Syrian President Bashar al-Assad out of fear they would be targeted by Turkish forces. Russia, which along with Iran backs the Assad regime, has also sent soldiers to the area.

"Syria is protecting the Kurds, that's good," Mr. Trump said. "Syria may get help from Russia and that's fine....There's a lot of sand to play with."

"I wish them all a lot of luck," he added.

Sen. Lindsey Graham (R., S.C.), who has criticized Mr. Trump's decision to withdraw troops, said the remarks "completely undercut Vice President Pence and Sec. Pompeo's ability to end the conflict." He added in a Twitter message: "I fear this is a complete and utter national security disaster in the making and I hope President Trump will adjust his thinking."

The House of Representatives on Wednesday passed a bipartisan resolution opposing Mr. Trump's decision to withdraw U.S. troops, urging the administration to contain the fallout from Turkey's incursion. The measure -- which passed by a 354-to-60 vote -- was the first formal step lawmakers have taken to register their criticism of the pullout.

Mr. Erdogan on Wednesday said Turkish troops would stop the offensive only if the Kurdish militia that Ankara views as a terrorist threat drops the fight and leaves areas it controls along the Turkish-Syrian border by Wednesday night.

On Wednesday, the U.S, military said two F-15E jet fighters carried out an airstrike to destroy an ammunition-storage facility and other parts of the Syrian headquarters of the American campaign to destroy Islamic State after pulling its forces from the base.

Col. Myles Caggins, a spokesman for the U.S.-led coalition overseeing the fight against Islamic State, said the airstrikes were intended to "reduce the facility's military usefulness."

The decision to target the base, which included warehouses used to train-and-equip the Kurdish-led fighters, came after Turkish-backed forces moved on the facility on Tuesday.

As the Turkish-backed forces moved closer to the LaFarge Cement Factory facility south of Kobane, the Kurdish-backed forces set fire to their part of the base and fled, Col. Caggins said.

The U.S. used Apache helicopters and F-15 jet fighters to intimidate the Turkish-backed fighters and deter them from getting closer to the base, U.S. officials said.

After the show of force, the U.S. military pulled its forces out of the base and carried out what it called a "pre-planned precision airstrike" before Turkish-backed fighters could take control of the facility.

The Trump administration is trying to contain the escalation of hostilities following Mr. Trump's Oct. 6 order to withdraw the roughly 1,000 U.S. soldiers stationed in northeastern Syria. The arrival of Messrs. Pence and Pompeo is part of Washington's efforts to claw back control of events that have diminished the U.S.'s leverage to shape Syria's post-conflict future and made Russian President Vladimir Putin the leading power broker.

After Mr. Erdogan made contradictory statements, his office clarified on Wednesday that the president would meet with Messrs. Pompeo and Pence. But Mr. Erdogan criticized Washington's efforts to mediate.

"Honestly, I do not find it appropriate that a country like the U.S. acts as a mediator between a terrorist organization and an ally like the Turkish Republic," Mr. Erdogan told Turkish media late Tuesday while flying back from Azerbaijan.

On the ground in northeastern Syria, troop movements reflected the fast-changing geopolitical dynamic sparked by Mr. Trump's Oct. 6 order to withdraw the U.S. forces.

Mr. Erdogan said the Turkish military had pushed more than 20 miles into Syria and taken control of the strategic M4 highway, which runs parallel to the border with Turkey and was one of the main supply lines for Kurdish forces. Meanwhile, Russian forces filled the void created by departing U.S. troops, notably in the border city of Manbij, were they began patrolling the line between Turkish and Syrian armies.

After Mr. Trump withdrew from the partnership with Kurdish fighters, the militia sought to shield itself from the Turkish offensive by striking an alliance with Mr. Assad's government.

Highlighting Russia's growing influence in the region, the Kremlin said Mr. Putin had invited Mr. Erdogan to come to Moscow to discuss the situation in Syria. The Turkish president's office said he will meet his Russian counterpart in Sochi next Tuesday.

Mr. Trump has invited Mr. Erdogan to the U.S. in November. Mr. Erdogan's office has acknowledged the invitation but hasn't confirmed if he will make the trip.

The Turkish president has said he is increasingly straining to follow the positions of his U.S. counterpart. "When we look at Mr. Trump's Twitter statements so far, we find ourselves in a situation where we can't follow them anymore," Mr. Erdogan was quoted as saying in his interview with Turkish media. "We can't keep up with them."

Mr. Trump's national-security adviser, Robert O'Brien, was expected to arrive in the Turkish capital on Wednesday for a preparatory meeting with Turkish Foreign Minister Mevlut Cavusoglu.

For the U.S., "goal No. 1 is to carry out diplomacy, to try to find a cease-fire and get the situation under control," a senior Trump administration official said.

The official denounced Ankara's suggestions that the U.S. had provided Kurdish-led forces in Syria with heavy weapons, saying it has given the Syrian Democratic Forces mainly small arms and mortars.

Turkey's incursion has displaced some 130,000 people from their homes in northeast Syria since it began one week ago, the United Nations said. The majority have remained within the country, moving away from the border to seek sanctuary from the fighting.

Write to David Gauthier-Villars at David.Gauthier-Villars@wsj.com, Vivian Salama at vivian.salama@wsj.com and Dion Nissenbaum at dion.nissenbaum@wsj.com

(END) Dow Jones Newswires

October 16, 2019 18:35 ET (22:35 GMT)

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