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 ISIS militants repelled the New Syrian Army from an air base which the rebels had briefly captured earlier in the day. ISIS 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. […]