The mother of 21-year-old nurse Yulia Izotova mourns at her funeral in Kramatorsk, eastern Ukraine May 5, 2014. Witnesses say Izotova was killed by shots from a Ukrainian military column on the road from Slaviansk to Kramatorsk, joining a small but gradually growing list of dead in a month-old uprising. [Photo/Agencies]

ODESSA/SLAVIANSK, Ukraine - Pro-Russian rebels shot down a Ukrainian helicopter in fierce fighting near the eastern town of Slaviansk on Monday, and Kiev drafted police special forces to the southwestern port city of Odessa to halt a feared westward spread of rebellion.

Ukraine said the Odessa force, based on "civil activists", would replace local police who had failed to tackle rebel actions at the weekend. Its dispatch was a clear signal from Kiev that, while tackling rebellion in the east, it would vigorously resist any sign of a slide to a broader civil war.

Odessa, with its ethnic mix from Russians to Ukrainians, Georgians to Tatars a cultural contrast to the pro-Russian east, was quiet on Monday. Ukrainian flags flew at half mast for funerals of some of the dozens killed in clashes on Friday.

But in the east, fighting intensified around the pro-Russian stronghold of Slaviansk, a city of 118,000, where rebel fighters ambushed Ukrainian forces early in the day.

The Interior Ministry said five paramilitary police were killed. Separatists said four of their number had also died.

The sound of an air-raid siren could be heard in the centre of Slaviansk, and a church bell rang in the main square.

Russia's foreign ministry called on Kiev to "stop the bloodshed, withdraw forces and finally sit down at the negotiating table". It also published an 80-page report detailing "widespread and gross human rights violations" in Ukraine over the past six months for which it blamed the new government and its Western allies.

CONCERNS FOR KIEV

Russia denies Ukrainian and Western charges it is seeking to undermine the country of 45 million and using special forces to lead the insurgency, as it did before annexing Crimea in March.

German Foreign Minister Frank-Walter Steinmeier said he feared neither side could now control forces unleashed.

"I'm convinced we are struggling against a situation that has taken on a dynamic of its own. There are groups in eastern Ukraine that are not listening to either Kiev ... or Moscow."

The self-declared pro-Russian mayor of Slaviansk Vyacheslav Ponomarev said: "(The Ukrainians) are deploying ever more forces here. Recently there was a parachute drop... For us, they are not military, but fascists."

Ukraine's Defence Ministry said rebels had shot down a military helicopter, the fourth since Friday, with heavy machine gun fire. The helicopter crashed into a river and the crew was rescued but there were no details of their condition.

Diana, 15, who lives near Slaviansk in a single-storey house at the strategic junction of the road between Kharkiv and Rostov, said she saw Ukrainian tanks fire on rebel cars. A fuel tank at a petrol station exploded and fighters fired at houses.

"My father was injured in the head by glass splinters. It's terrifying. There's just nowhere to live now. Everything is broken, our television, our computer; they shot at our car."

The violence in Odessa marked a watershed for Ukraine.