Hello and welcome to our live coverage of the unfolding situation in eastern Ukraine, where the national government has launched an "anti-terrorist operation" in the city of Sloviansk. Ukrainian forces are trying to take back control of the local police HQ, which is being held by pro-Russian activists.
Yesterday armed men took over police stations and official buildings in Sloviansk and two other eastern towns - Kramatorsk and Druzhkovka. Russia has warned that any use of force in eastern Ukraine could scupper crisis talks due later this week.
There were reports of gunfire and explosions in Sloviansk this morning and video purportedly showing a Ukrainian helicopter flying low over the city has also surfaced - but so far we've had no confirmed reports of military movement in the city.
Victor, Moscow, Russia
emails: People in East Ukraine wish only one thing, a referendum, they have had enough of feeding corrupted authorities.
Ben Judah, a British author and Russia analyst, has been talking to the BBC World Service this morning about the events in eastern Ukraine. He believes the unidentified gunmen that took control of several police stations in the region yesterday are part of "a world class special operations campaign" led by the Russians. "Russia's invasion of Ukraine has in a a sense already begun," Mr Judah added.
Some images have begun to emerge from the storming of a police station in Kramatorsk yesterday. Russian news agency Itar Tass has published several pictures of the "people's militia" that forced local police to hand over the building. There is also video of the moment the men arrived. They fired warning shots and barged policemen out of their way in what looked like a fairly professional, co-ordinated offensive.
Most of the armed men have been eager to avoid photos, but one group in Sloviansk were happy to pose for a picture taken by photographer Maxim Dondyuk.
BBC Monitoring reports that Serhiy Taruta, the governor of Donetsk, has said that "all legitimate means" will be used to restore order in the region. In a statement, he said the takeover of police stations and government buildings were "acts of terror" and would be dealt with by the security services. "Unidentified armed men have been capturing police departments across the region, pillaging them and arming the local population," he said.