Kyiv has sent an elite national guard unit to its southern port of Odesa in a bid to stop the spread of fighting between government troops and pro-Russian separatist forces in eastern Ukraine that has killed combatants on both sides, RFE/RL reports.

Kyiv said the special forces would replace local police who had failed to control pro-Russian activists in Odesa during the weekend. 

Odesa saw some of the worst violence in Ukraine's crisis on May 2 when supporters of the government in Kyiv and pro-Russian groups clashed for much of the day.

Pro-Russian supporters fled inside a trade union building that subsequently caught fire, killing dozens of people inside.

The deployment of special forces to Odesa on May 5 came as clashes in the east killed four Ukrainian soldiers and as a government helicopter was shot down.

It was the third helicopter to be downed by pro-Russian forces in eastern Ukraine since Kyiv launched military operations there last week in an attempt to gain control of cities and towns seized by separatists.