(CNN)The battle for Aleppo — once Syria’s commercial heart — is intensifying, and video has surfaced appearing to show thousands of civilians streaming out of the devastated city.

CNN could not independently verify the authenticity of the video, 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.

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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.

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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.

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