40,000 flee Aleppo as Turkish border remains closed

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

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

The exodus comes as the battle for Aleppo - once Syria's commercial centre - is intensifying, and video has surfaced appearing to show thousands of civilians streaming out of the devastated city.

The authenticity of the video has not yet been verified, but the United Nations Office for the Coordination of Humanitarian Affairs said via Twitter Friday that 40,000 people have been displaced by the ongoing fighting around Aleppo.

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

In the past few days, the Syrian army backed by Russian air power has made a series of gains in the area.

Reports said forces loyal to Syrian President Bashar al-Assad's government, crucially aided by Russian air power, have cut the city off from supplies and are advancing.

Increasingly intensive Russian airstrikes are pushing thousands of Syrians north, away from the northern outskirts of the once bustling city, according to the National Coalition of Syrian Revolution and Opposition Forces, the main opposition group.

The Syrian Observatory for Human Rights, a UK-based monitoring group, says about 120 fighters on both sides were killed around the town of Ratyan, north of Aleppo on Friday.

Turkey is providing food, shelter and blankets to thousands of civilians who are stranded on the Syrian side of the border because of the fighting.

However the Turks have so far refused to open the border crossing.

EU Enlargement Commissioner Johannes Hahn on Saturday urged Turkey to open the frontier.

"The Geneva convention is still valid which states that you have to take in refugees." Hahn said, as EU foreign ministers prepared to discuss the crisis in Amsterdam.

On Thursday 60 donor countries meeting in London pledged billions of dollars to ease the plight of Syrian refugees - with the EU agreeing to spend €3 billion.

About 4.6 million people have fled Syria during the five-year civil war. Another 13.5 million are said to be in need of humanitarian assistance inside the country.

Turkey hosts the largest number of refugees - 2.5 million.