At least 4 Ukrainian soldiers killed in offensive against pro-Russian rebels

Ukraine's military suffered heavy casualties in a stepped-up offensive on pro-Russian rebels yesterday, as Europe and the head of the UN made a last-ditch diplomatic effort to reel the country back from the brink of civil war.

At least four Ukrainian servicemen were killed and 30 injured battling heavily armed insurgents around the flashpoint eastern town of Slavyansk as Russia warned the violence was putting peace in Europe in peril.

The interior ministry in Kiev said the pro-Russian gunmen controlling the town were using civilians as human shields and were shooting from houses, some of which were on fire.

"They are waging a war on us, on our own territory ... my mission is to eliminate the terrorists," Interior Minister Arsen Avakov told reporters near Slavyansk.

The head of Ukraine's national guard, Stepan Poltorak , said: "We have bottled them up in the centre" of Slavyansk, but added that "our adversaries are well-trained and well-equipped".

The advance on Slavyansk was part of a wider military operation in the east to root out the separatist insurgents, who are holding more than a dozen towns. The authorities retook control of the television tower near Slavyansk but lost a helicopter. The pilots survived.

Russia, which denies any hand in the violence, warned in a foreign ministry report yesterday that the unrest in Ukraine was now "fraught with such destructive consequences for Europe's peace, stability and democratic development that it is absolutely necessary to prevent it".

The report accused Ukrainian "ultra-nationalists" - who Moscow claims control Kiev's government - of rights violations on a "mass" scale. But Ukraine's interim president declared that it was Russian meddling that had brought war to his country.

Oleksandr Turchynov warned that pro-Russian provocateurs might stage violence in Kiev during Friday's celebrations marking the Soviet victory over Nazi Germany in the second world war.

"War is in effect being waged against us, and we must be ready to repel this aggression," said Turchynov, who has placed Ukraine's armed forces on combat alert and reintroduced conscription amid fears of a Russian invasion.

The chairman of the Organisation for Security and Co-operation in Europe, Didier Burkhalter, was due in Moscow tomorrow amid calls for his group to mediate between Kiev and eastern separatists.