IRBIL, Iraq -- Vice-President Mike Pence worked to reassure the United States' Kurdish allies in an unannounced trip to Iraq on Saturday, the highest-level American trip since President Donald Trump ordered a pullback of U.S. forces in Syria two months ago.

Flying in a C-17 military cargo aircraft, Pence landed in Irbil, capital of Iraq's semiautonomous Kurdish region, to meet with Iraqi Kurdistan President Nechirvan Barzani.

The visit was meant to hearten the United States' regional partners in the fight against the Islamic State group after the U.S. pulled troops from northern Syria, leaving America's Kurdish allies there to face a bloody cross-border Turkish assault last month.

Asked by reporters if the United States was facing a sense of betrayal from Iraqi and Syrian Kurdish allies over Trump's actions in Syria, Pence said both groups, including Syrian Kurdish forces "who fought alongside us," had no doubts about the U.S. commitment to them. "It's unchanging," Pence said.

Earlier, Pence received a classified briefing at Iraq's Al-Asad Air Base, from which U.S. forces are believed to have launched the operation in Syria last month that resulted in the death of Islamic State leader Abu Bakr al-Baghdadi. Pence also spoke by phone with Iraqi Prime Minister Adel Abdul-Mahdi.

Underscoring Pence's message that American military partnership with Syrian Kurdish forces is ongoing, the U.S.-led coalition said Saturday that its forces, along with hundreds of Syrian Kurdish commandos, had jointly carried out the largest operation against the Islamic State in eastern Syria since the U.S. pullback began in early October.

Friday's operation in southeastern Syria's Deir el-Zour province captured dozens of Islamic State militants, cleared enemy compounds and seized weapons and explosives, the U.S.-led coalition said. Operations against Islamic State militants in Syria had been disrupted, but not totally halted, because of the U.S. troop pullback and Turkey's invasion.

Pence's trip Saturday was his second to the region in five weeks. Trump deployed him on a whirlwind journey to Ankara, Turkey, last month to negotiate a cease-fire after President Recep Tayyip Erdogan seized on the U.S. withdrawal to launch the offensive on U.S.-allied Kurdish fighters in northern Syria. Trump's move had sparked some of the most unified criticism of his administration to date, as lawmakers in both parties accused Trump of forsaking longtime Kurdish allies and inviting Russia and Iran to hold even greater sway in the volatile region.

When the U.S. forces withdrew, Syria's Kurds -- seeking protection from their No. 1 enemy, Turkey -- invited Syrian government and Russian forces into parts of northeastern Syria where they had not set foot in years. More are now deploying along large parts of the border region under a Russian-Turkish deal, including to at least one former U.S. garrison in northern Syria.

The Ankara agreement required Syrian Kurds to vacate a swath of territory in Syria along the Turkish border in an arrangement that largely solidified Turkey's position and aims.

Pence hailed the cease-fire as the way to end the bloodshed caused by Turkey's invasion.

But Syrian-led Kurdish forces say the cease-fire is persistently violated. Fighting raged Saturday between them and Turkey-backed forces outside the Syrian town of Ein Issa, once home to U.S. bases and the Kurdish administration.

A senior Syrian Kurdish official was critical Saturday of Washington's lack of response to Turkey's violations of the cease-fire.

Limiting the U.S. partnership to military co-operation over a limited area with the Syrian Kurdish fighters, "while condoning the killing of civilians, is not a very honest relationship and co-operation," the official, Ilham Ahmed, said.

On Nov. 13, Trump feted Erdogan with a White House visit over the objection of a bipartisan group of lawmakers who argued Erdogan should be denied the honour of a West Wing visit in the aftermath of the invasion and because of his decision to purchase Russian-made surface-to-air missiles over the objection of NATO allies.

In neighbouring Syria, after declaring the near-complete withdrawal of U.S. forces from Syria, Trump decided that roughly 800 would stay to keep eastern Syria's oil fields from falling back into the hands of the Islamic State.

Trump also agreed to keep about 150 U.S. troops at a base in southern Syria as a check on Iranian influence in the region.

While Trump has claimed that the U.S. was now "keeping" the oil in Syria, Pentagon officials indicated the U.S. presence is not intended to improve the oil infrastructure but to keep it in the hands of the Kurdish-led Syrian Democratic Forces.

Pence, joined on the trip by his wife, Karen Pence, also greeted U.S. troops ahead of the Thanksgiving holiday, serving turkey and accompaniments to hundreds of troops at the two locations.

"While you come from the rest of us, you're the best of us," Pence told service members in a dusty hangar at Al-Asad. He said the Trump administration is working to secure another pay increase for the armed services and suggested the ongoing impeachment inquiry in Washington was slowing the way.

"Partisan politics and endless investigations have slowed things down in D.C.," Pence said.

Pence's visit to Iraq comes as the country has been plagued by widespread anti-corruption protests. At least 320 protesters have been killed and thousands have been wounded since the unrest began on Oct. 1.

Pence spoke by phone with Abdul-Mahdi after the Iraqi leader declined an invitation to meet with Pence at the air base when security concerns prevented Pence from travelling into Baghdad.

Pence encouraged the Iraqi government to show restraint with the protesters.

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Associated Press writers Samya Kullab in Baghdad and Sarah El Deeb in Beirut contributed.