The number of Syrians trying to cross into Turkey amid an upsurge of fighting in northern Syria has nearly doubled, a Turkish official says.

The governor of the Turkish border province of Kilis said 35,000 refugees had reached the border area – up from an estimated 20,000 on Friday.

Turkey says it is prepared to help the refugees but the frontier remains shut.

They are fleeing a Syrian government offensive on rebel-held positions near the northern city of Aleppo.

In the past few days, the Syrian army – backed by Russian air strikes – has made a series of gains around Syria’s largest city.