BEIRUT: Syrian Kurdish and rebel forces, backed by U.S.-led air strikes, advanced Thursday into Raqqa province, where ISIS has its de facto capital, an activist group said.

"The YPG [Kurdish People's Protection Units] and rebel forces captured 19 villages in Raqqa province," said the Syrian Observatory for Human Rights.

"The U.S.-led international coalition played a key role in the advance, bombing the ISIS positions and forcing its fighters to withdraw," said Observatory director Rami Abdel Rahman.

The advance comes as Kurdish and rebel forces push outwards from the border town of Kobani, from which they expelled ISIS forces after more than four months of fighting.

Since driving ISIS out of Kobani on January 26, Kurdish and allied forces have taken much of the surrounding countryside in northern Aleppo province and begun pushing east into neighboring Raqqa province.

They have captured some 242 villages around Kobani, including the 19 in Raqqa province, according to the Observatory.

They are now 25 kilometers (15 miles) from Tal Abyad, another Kurdish-majority border town overrun by ISIS.

Located 65 kilometers east of Kobani, the town is used by ISIS fighters to cross into Turkey.