BEIRUT – U.S. aircraft ferried Syrian Kurdish fighters and allied forces behind Islamic State (I.S.) lines on Wednesday to spearhead a major ground assault on a strategic town held by the extremist group outside its self-declared capital, Raqqa, the Pentagon said, marking the first time U.S. forces have provided airlift for local forces on a combat operation in Syria.

The airlift was part of what Pentagon spokesman Eric Pahon described as a large, high-priority offensive to secure the area around Tabqa and the associated Tabqa Dam on the Euphrates River which supplies electric power to the area.

“This is a significant strategic target,” said Pahon. If successful, the operation would “basically cut ISIS off” from the western approaches to Raqqa.

The U.S. has significantly widened its footprint in northern Syria in the past few weeks as it prepares for the operation to push the militants from Raqqa, deploying a Marine artillery unit and a few dozen Army Rangers in addition to special operation troops and advisers to assist the local forces.

Wednesday’s airlift, which Navy Capt. Jeff Davis, a Pentagon spokesman, described as a first, displayed a new level of commitment to Syria’s Kurds, whose partnership with the U.S. in fighting I.S. has prompted difficult discussions with Turkey, which sees the militants as a national security threat.

Col. Joseph Scrocca, a spokesman for the U.S.-led coalition that is overseeing the counter-I.S. campaign in Syria and Iraq, said multiple U.S. helicopters and other aircraft were used to land the Syrian fighters south of Tabqa. The U.S. also provided artillery fire from a Marine contingent, as well as close air support by U.S. Army Apache helicopters, he said.

“This is pretty major,” he said, adding the fight for the dam, the town and the airfield is expected to last at least a couple of weeks. He would not say how many Syrian fighters were involved. In contradiction to earlier U.S. statements, Scrocca said some of the Syrian fighters who were airlifted to Tabqa were Kurds. He said 75 to 80 percent of the fighters were Syrian Arabs.

The U.S.-backed, Kurdish-led Syrian Democratic Forces confirmed the airlift and said their fighters seized four villages south of the Euphrates and cut the main artery between Raqqa and northwestern Syria.

The group said in a statement on social media that U.S. infantry were also airlifted into the area of operations. The Pentagon initially said that the airlift was for Syrian fighters only, but Scrocca later said that an undisclosed number of U.S. military advisers were also flown in. Both said that no U.S. troops were involved in fighting on the front line.

Tabqa lies 45 kilometers (28 miles) west of Raqqa. The Islamic State group controls the town as well as the dam and a military airfield nearby.

“This is a big operation,” Pahon said, adding that Tabqa is an important IS-held area because of the dam that provides electricity to the area. He said IS has controlled the area since 2013 and used it for a combination of purposes, including as a prison for high-profile hostages and as a training camp and headquarters.

Retaking the dam would go a long way in isolating Raqqa and is a crucial step ahead of the assault on the city. There has been concern the militant group would destroy the dam, flooding the region.

The airlift coincided with a meeting in Washington that brought together the U.S. and top officials from 68 nations to assess the fight to retake Mosul, Iraq’s second largest city, from IS and advance on Raqqa.

Secretary of State Rex Tillerson told the coalition’s first ministerial gathering since President Donald Trump took office that the Trump administration was still refining its strategy on Syria but the United States’ number one goal in the region was to defeat I.S.

Also Wednesday, the U.S.-led coalition against the Islamic State group said it was looking into reports that a U.S.-led coalition aircraft may have struck a shelter for the displaced in the village of Mansoura, also held by I.S.

Syrian activists said Wednesday that dozens of people were killed or missing after an airstrike the day before leveled a school near the I.S.-held city of Raqqa, where displaced families had sought refuge.

The activist-run group Raqqa is Being Slaughtered Silently said some 50 families had been sheltering at the school in the northern Syrian village of Mansoura and that their fate was still unknown. Mansoura is 26 kilometers (16 miles) west of Raqqa and is under I.S. control.

The Britain-based Syrian Observatory for Human Rights said 33 bodies had been pulled from the rubble. The two organizations rely on local contacts to smuggle news out of Islamic State-held territory.

It was not immediately clear who carried out the airstrike. Syrian Kurdish forces have been advancing on Raqqa under the cover of U.S.-led coalition airstrikes and are now eight kilometers (five miles) north of the city. Syrian and Russian aircraft have also carried out strikes against the I.S. group.

Elsewhere in Syria, insurgents advanced to within a few kilometers of the government-held city of Hama in a new offensive spearheaded by an al-Qaida-linked group.

The activist-run Hama Media Center said the rebels had reached the village of Khatab, 10 kilometers northwest of Hama city.

The offensive coincides with a concentrated effort by opposition forces to breach government lines in the eastern neighborhoods of the capital, Damascus. That operation is also spearheaded by the al-Qaida-linked Levant Liberation Committee.

In Damascus, the insurgents were pinned down in industrial zones in the city’s east. Government airstrikes and artillery fire echoed through the capital, and smoke could be seen rising above the opposition-held Jobar neighborhood. Residents close to the front lines on the government side were seen leaving their buildings with whatever belongings they could pack in suitcases.

The uptick in fighting precedes the resumption of U.N.-mediated talks between the government and the opposition in Geneva, slated for Thursday.

U.N. Special Envoy to Syria Staffan de Mistura called the developments “alarming,” but said the invited delegations would be in attendance “with, I hope, serious intentions to follow up the political process.”

He spoke to reporters in Moscow, following a meeting with Russian Foreign Minister Sergei Lavrov.

Lavrov accused militants of carrying out more “terrorist attacks,” which he said were “aimed at disrupting or complicating the Geneva talks.”

Russia is a steadfast ally of Syrian President Bashar Assad.

PHILIP ISSA

ROBERT BURNS