Ukraine tensions: A warning siren blares in rebel-held Donetsk

Footage shows people running in the streets of Donetsk in Ukraine as a warning siren blared across the city.

The region's separatist leader has announced that some residents will be evacuated from the city.

Rebels who refuse to recognise the Ukrainian government in Kiev seized territory in Donetsk in an uprising in April 2014.

Since then, thousands of people have died in fighting between the rebels and Ukrainian government forces.

Moscow has denied sending troops and weapons to the rebels, instead admitting that Russian "volunteers" are aiding the rebels.

Western leaders have been warning that Russia is looking for a pretext to invade Ukraine.