BEIRUT — Islamic State militants on Wednesday pushed back U.S.-trained Syrian rebels from the outskirts of a town on the Iraqi border, in a setback to a budding offensive that aims to sever the militants' transit link between the two countries, a rebel spokesman said.
The Islamic State-linked Aamaq news agency said IS militants repelled the New Syrian Army from an air base which the rebels had briefly captured earlier in the day. IS said it seized 15 hostages and ammunition, and was still advancing against the rebels.
Earlier Wednesday, the Pentagon-trained force entered the Hamdan air base — northwest of the border town of Boukamal — following intense clashes, rebel spokesman Mozahem al-Saloum said.
He said airborne fighters were dropped from coalition helicopters on Boukamal's southern edge, helping the rebels advance. The Britain-based Syrian Observatory for Human Rights, which relies on local activists, confirmed the account.
The Observatory's chief, Rami Abdurrahman, said foreign airborne fighters were also dropped to the north, enabling the takeover of the base. The rebels were heavily backed by U.S.-led coalition airstrikes and were coordinating their fight with Iraqi tribesmen and forces on the other side of the border, al-Saloum said.
The U.S.-led coalition has been carrying out airstrikes against IS in Iraq and Syria since 2014 and 300 U.S. Special Forces are embedded with a Kurdish-led militia in northern Syria. It was not immediately clear whether U.S. forces were involved in the Boukamal offensive or what other nations might be taking part in it. The U.S. Central Command said coalition jets carried out several airstrikes on IS targets in the Boukamal area.
Col. Chris Garver, a spokesman for the U.S.-led coalition in Baghdad, said in a briefing that the U.S has provided advice and assistance to the New Syrian Army as well as airstrikes in both Syria and Iraq in support of the operation. He did not mention the setback or the helicopter-borne movement of Syrian fighters.
The Observatory said several hundred rebels from different factions were involved in the offensive, which began on Tuesday. It said IS fighters have dug trenches and planted land mines south of the town.
Al-Saloum acknowledged that the New Syrian Army forces were unable to keep the base and other outposts to the south, near the Qaim border crossing with Iraq, but said the offensive would continue.
Wednesday's setback was another blow to the rebel group. Two weeks ago, Washington accused Russian aircraft of bombing the rebels near the Iraqi border. Russia has been carrying out airstrikes in support of Syrian President Bashar Assad's forces since September.
IS seized much of the Iraq-Syria border in its 2014 blitz, along with large swaths of territory in both countries, declaring an Islamic caliphate. But IS has in recent weeks been losing ground, both in Iraq and in Syria.
The U.S.-backed and Kurdish-led forces have besieged Manbij, an IS stronghold in northern Syria, while Iraqi forces have taken Fallujah, in Iraq's western Anbar province, from the Sunni extremist group.
Meanwhile, aid was delivered to the besieged Syrian towns of Zamalka and Irbin for the first time since 2012, when the two rebel-held areas east of Damascus were besieged by government forces. The 37-truck convoy organized by the International Committee of the Red Cross, the U.N. and the Syrian Arab Red Crescent carried enough food and medical aid for 20,000 people.
Further north, another joint convoy carrying food and medicine was delivered to the besieged suburb of west Harasta, which has a population of about 12,500, according to ICRC spokeswoman Ingy Sedky.
Associated Press writer Robert Burns in Washington contributed to this report.