BEIRUT (AP) — Members of al-Qaida's branch in Syria launched an attack early Friday on the headquarters of a rebel faction in northern Syria believed to have been trained by the U.S. government, killing at least five fighters and wounding more than a dozen, the militants and an activist group said. The Nusra Front, which has also abducted several members of the faction known as Division 30, vowed to cut off "the arms" of the American government in Syria.

A statement issued in the name of Division 30, said its fighters prevented Nusra Front gunmen from storming their head office and added that the fighting is still ongoing.

The Nusra Front said in a statement later Friday that it has detained some members of Division 30, claiming they were trained by the CIA and that the previously obscure group's fighters had entered Syria recently "to carry out the projects and interests of America in the region and to fight what they call terrorist organizations."

The fighting came a few days after the U.S. and Turkey announced the outlines of a deal to help rebels push the Islamic State group 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 U.S. military official on Friday seemed to deny any American connection to Division 30, saying that no member of a U.S.-backed rebel faction had been abducted.

"That report had nothing to do with the Syrian fighters we trained and equipped," said Marine Corp. Brig. Gen. Kevin Killea, chief of staff of the U.S.-led coalition. "We have nothing to confirm any reports that talk about injured, killed in combat. I can tell you with certainty we know that none of them have been captured."

However both the Britain-based Syrian Observatory for Human Rights and Abdul-Jabbar Abu Thabet, commander of Aleppo Swords Battalion — a moderate faction that is fighting both Syrian government forces and IS — said the members of Division 30 were trained by the U.S. in Turkey.

Abu Thabet said Nusra Front has been referring to Division 30 as "agents of the Americans."

Rami Abdurrahman, who heads the Observatory, said that the rebel group's perceived American connection made it a target for the Nusra Front.

"They are trying to liquidate any group that has links to the West," he said.

The Observatory added that warplanes believed to be from the U.S.-led coalition attacked Nusra Front positions in the area after the fighting broke out.

The Nusra Front, which has in the past targeted rebel groups backed by the United States, said coalition warplanes struck their positions in the area of fighting with more than 10 missiles that killed and wounded several fighters. It said the airstrikes showed "the clear cooperation and coordination" between the U.S. and Division 30.

In the past year, the extremist group has routed the U.S.-backed Harakat Hazm rebel group and the Syria Revolutionary Front from their main northern strongholds in Idlib province, dealing a blow to U.S. efforts to arm and train moderate Syrian rebels.

The Nusra Front statement said the U.S. had extended its arms inside Syria over the past two years, and in response, "the Mujahedeen cut these arms."

The Observatory and Abu Thabet said Friday's fighting was concentrated south of the Syrian town of Azaz on the border with Turkey.

Nusra Front's attack came two days after the extremists abducted Col. Nadim al-Hassan, commander of Division 30 and seven of his men, according to the rebel group, the Observatory and the Nusra Front itself.

Abu Thabet and Division 30 said Nusra Front gathered its forces in the area near Azaz on Thursday saying that they were heading to fight Kurdish fighters in the nearby region of Ifrin. Instead, they launched an attack on the Division 30 command near Azaz, they said.

Division 30 called on the Nusra Front to stop their attack "to avoid bloodshed between Muslims" and said five of its fighters were killed and 18 were wounded in the fighting. The Observatory said 18 Nusra Front fighters were killed in the fighting and the airstrikes.

The Nusra Front vowed to defend Syrians against President Bashar Assad's government as well as "any American agent."

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 as few than 100 have entered training taking place at bases in Jordan and Turkey. Fewer than 60 have recently entered Syria.

In eastern Syria, the U.S. backed coalition destroyed three bridges on the Euphrates river including one close to the Syrian-Iraqi border, according to the Observatory and the Local Coordination Committees activist group.

Earlier in July, the coalition attacked 16 bridges in and near the northern Syrian city of Raqqa, the Islamic State group's de facto capital, in order to prevent the extremists from moving military capabilities in Syria and Iraq.

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Associated Press writer Ken Dilanian in Washington contributed to this report.