There are conflicting reports over the number of deaths in what Kyiv has called its “anti-terrorist” operation around the city of Slovyansk.

A senior official in Kyiv said the operation has been suspended, at least partially, to re-organise, but also because of a heightened risk of Russia sending in troops.

The self-styled Mayor of Slovyansk raged at an illegal checkpoint over the one death that could be confirmed, although there were earlier reports that up to seven pro-Russian gunmen had died as the Ukrainian army dismantled several illegal roadblocks around the city of 130,000 people.

The early morning attack outside Slovyansk came as Ukrainian police said they had regained control of a government building in the port city of Mariupol and that the military had repulsed an attack on a military base in Artemovsk.

A Ukrainian helicopter gunship was seen hovering over one checkpoint for some time, and the Ukrainian army units appeared well-armed and organised in what has been their most serious show of strength since the crisis began.