Ukraine crisis: 'A lot of tension and worry in Donetsk'

Russian President Vladimir Putin has warned that Ukraine is "on the verge of civil war" after Kiev sent in troops against pro-Russia separatists.

Ukraine announced the start of an "anti-terrorist operation" in the east of the country on Tuesday.

BBC correspondent David Stern is in Donetsk in eastern Ukraine and says there is, "a lot of tension and a lot of worry about what is going to happen next".