Syrian Kurdish fighters have recaptured more than 10 villages seized by ISIL takfiri group north of its de facto capital of Raqqa city.

Syrian Kurdish fighters have recaptured more than 10 villages seized by the so-called 'Islamic State of Iraq and the Levant' (ISIL) takfiri group north of its de facto capital of Raqqa city, aided by US-led coalition air strikes, the Syrian Observatory for Human Rights reported on Tuesday.

Intensified air strikes across northern Syria and clashes on the ground have killed at least 78 ISIL fighters since Sunday night, the opposition Britain-based Observatory said.

The strikes are some of the most sustained since they began in September, according to US officials who say they are aimed at curbing the militants' ability to operate out of Raqqa and to prevent it from fighting back against Kurdish advances.

But, on Tuesday, the ISIL was still in control of Ain Issa, the Observatory said. The town, 50 km (30 miles) north of Raqqa city, was seized by ISIL terrorists from the Kurdish YPG militia in an attack on Monday.

The YPG, a militia operating mostly in predominantly Kurdish areas of northern Syria towards the Turkish border, has emerged as the only significant partner in Syria for US-led alliance fighting to tackle ISIL both there and in Iraq.

The YPG captured Ain Issa on June 23.