Slaviansk: Ukraine’s military has launched assaults to retake rebel-held eastern towns in which up to five people were reported killed, a move Russian President Vladimir Putin warned would have ‘‘consequences’’.

Thursday’s offensive sent international tensions soaring and oil prices up, raising the prospect of Russia making good on its threat of a massive response in the ex-Soviet republic.

Ukrainian security force officers at a checkpoint set on fire and left by pro-Russian separatists near Slaviansk. Credit:Reuters

In Slaviansk, a flashpoint east Ukrainian town held by rebels since mid-April, armoured military vehicles drove past an abandoned roadblock in flames to take up position, AFP reporters saw.

Shots were heard as a helicopter flew overhead, and the pro-Kremlin rebels ordered all civilians out of the town hall to take up defensive positions inside.