Syrian Kurdish and rebel forces, backed by US-led air strikes, advanced on Thursday, Feb 19 into Raqa province, where the jihadist Islamic State group has its de facto capital, a monitor said, according to Agence France-Presse.

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

"The US-led international coalition played a key role in the advance, bombing the IS 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 Kobane, from which they expelled IS forces after more than four months of fighting.

Since driving IS out of Kobane on January 26, Kurdish and allied forces have taken much of the surrounding countryside in northern Aleppo province and begun pushing east into neighbouring Raqa province.

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

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

Located 65 kilometres east of Kobane, the town is used by IS fighters to cross into Turkey.