BEIRUT (AP) — The leader of a U.S.-backed rebel group and several of his men have been abducted in northern Syria by the al-Qaida-affiliated Nusra Front, the rebel group and opposition activists said Thursday.

A statement issued in the name of the group, "Division 30," accused the Nusra Front of abducting Col. Nadim al-Hassan and several other members of the group in the northern Aleppo countryside. It called for their immediate release "to avoid bloodshed between Muslims."

There was no official comment from the Nusra Front, which has in the past moved against rebel groups backed by the United States. Last year, the extremist group routed the U.S.-backed Harakat Hazm rebel group and the Syria Revolutionary Front from their main northern strongholds in the Idlib province, dealing a blow to U.S. efforts to arm and train Syrian rebels.

The kidnapping, which occurred Wednesday night, came a few days after the U.S. and Turkey announced the outlines of a deal to help rebels push IS back from a strip of territory it controls along the Syrian-Turkish border, replacing it with more moderate rebels backed by Washington and Ankara.

A representative of "Division 30" said reports that the group was Western-backed were likely the reason behind the kidnapping. He declined to say whether his group was among those trained by the U.S., saying only: "The Division supports any side that helps Syria and the Syrians against Daesh." The representative spoke on condition of anonymity for security considerations. Daesh is an Arabic acronym for the Islamic State group.

The Britain-based Syrian Observatory for Human Rights said Thursday that al-Hassan is a Syrian army defector who now heads a brigade known as "Division 30."

Observatory director Rami Abdurrahman said members of "Division 30" were among rebels who were trained by the U.S. to fight the Islamic State group and recently entered Syria. He said al-Hassan was abducted near the border town of Azaz along with six members of the group as they were returning from a meeting Wednesday night.

Abu al-Hassan Marea, a Syrian activist who is currently in Turkey near the Syrian border, said the group was abducted by masked gunmen most likely belonging to the Nusra Front. He said the "Division 30" group had received training in Turkey, but did not know whether it was by the Americans.

White House spokesman Josh Earnest said he had seen the reports about the abductions, but could not confirm whether the captured rebels had been trained by the U.S.

The Obama administration has long struggled to find partners on the ground in Syria to work with in its war against the IS group.

A program for training moderate Syrian rebels to fight IS has been faltering. Pentagon officials say the vetting has been so strict that of an estimated 6,000 Syrian volunteers, only 1,500 have been declared qualified so far and that of those, few than 100 have been retained in the training taking place at bases in Jordan and Turkey. Fewer than 60 have recently entered Syria.

AP White House Correspondent Julie Pace in Washington contributed to this report.