Ukraine relaunched military operations against pro-Kremlin separatists, hours after US Vice President Joe Biden ended a two-day visit to Kiev in which he warned Russia over its actions in the former Soviet republic.

Meanwhile,the US Defence Department announced yesterday it was sending 600 troops to neighbouring Poland and to Baltic countries for exercises.

The latest moves underscored the severity of the crisis that has brought East-West relations to their most perilous point since the end of the Cold War.

Ukraine's acting president, Oleksandr Turchynov, late yesterday said he was ordering the military to restart operations against the rebels after the discovery of two bodies in the eastern rebel-held town of Slavyansk.

In a further slide back towards violence, which many fear could tip into civil war, a Ukrainian reconnaissance plane was hit by gunfire while flying above Slavyansk.

Pro-Moscow militants had taken over Kramatorsk's police station late Monday, extending their grip from the already occupied town hall.

Kiev, Washington and many EU countries see Moscow as pulling the strings in the Ukrainian separatist insurgency.