Kramatorsk lies some 17 kilometres (10 miles) to the south of the flashpoint town of Slavyansk, where the army mounted a major offensive on Friday that claimed at least nine lives, including two servicemen as rebels shot down a pair of army helicopters.

The dawn raid on Kramatorsk comes after Ukraine suffered its bloodiest day since the Western-backed government in Kiev came to power.

Ukraine’s acting president, Oleksandr Turchynov, said Friday that the military assault on the eastern city of Slovyansk was intended to protect civilians from “mercenaries of foreign states, terrorists and criminals who are taking hostages, killing and torturing people, and threatening the territorial integrity and stability of Ukraine.”

In addition to the nine killed in Slavyansk, more than 30 people died in what Avakov called a "criminal" blaze in the southern port city of Odessa following deadly clashes between pro-Russian militants and supporters of national unity.

Russia has an estimated 40,000 troops on the Ukrainian border and Kiev has reintroduced conscription and put its armed force on full combat alert, fearing an imminent invasion.