A Ukrainian jet has been filmed above the eastern city of Kramatorsk, where an airbase had been seized by pro-Russian activists.

The BBC's Gabriel Gatehouse at the airfield reported that gunfire could be heard. Ukraine's acting president says the base has now been "liberated".

However, locals reacted angrily when troops arrived in a helicopter from Kiev, calling for a referendum.

Ukraine's acting President Olexander Turchynov has announced the start of an "anti-terrorist operation" against pro-Russian rebels, who have seized buildings in about 10 towns and cities across Ukraine's eastern provinces.