Updated

U.S.-backed Syrian forces say Islamic State militants are putting up a desperate fight against their advances and have staged a counterattack from the tiny speck of land the extremists still hold in eastern Syria.

A commander with the U.S-backed Syrian Democratic Forces says the IS counterattack began overnight, from the west of a riverside pocket in the Syrian village of Baghouz where the Islamic State group has been making its last stand.

The commander says clashes were underway on Wednesday and that the Kurdish-led forces are repelling the IS counterattack. He spoke on condition of anonymity because he was not authorized to talk to the media.

A spokesman for the U.S.-backed forces, Adnan Afrin, says IS militants are putting up a "fierce resistance," firing mortar shells and rocket-propelled grenades.