The air strikes hit areas close to the town of Tal Tamer, south of the Turkish border, the Britain-based Syrian Observatory for Human Rights said.
It was the first time the U.S.-led coalition hit the area since last month, the Observatory’s founder Rami Abdulrahman said, citing sources on the ground.
The Kurdish YPG militia, backed by U.S.-led air strikes, had made significant gains in recent weeks against Islamic State in northern Syria, cutting an important supply route from territory controlled by the militant group in Iraq.
But Islamic State, which has declared a caliphate in areas it controls, appeared to try to seize back the initiative on Tuesday, attacking Kurdish fighters using tanks and heavy weapons close to the Turkish border.
The YPG has emerged as the main partner for the U.S.-led alliance fighting Islamic State on the ground in Syria.
Backed by Iraqi Kurdish peshmerga fighters and air strikes, the YPG defeated Islamic State in the border town of Kobani in January. The battle for Kobani was the first publicly-declared example of U.S.-led forces closely coordinating militarily with a ground force to battle Islamic State.
The United States says it wants to train and equip non-jihadist groups to fight the group elsewhere in Syria and the training was due to get underway in Jordan this month. It is not clear which rebel fighters it plans to train. (Reuters)