Ukraine peace talks failed today as hostilities intensified between government forces and Russian-backed separatists in the east.

The escalation in fighting has centred on the airport of the rebel stronghold of Donetsk, where rebel militia have renewed efforts to dislodge government troops.

Separatists say they have almost total control over the civilian terminal, but Ukrainian troops say they still hold parts of the building.

Representatives from Ukraine and Russia, separatist envoys and officials of the Organisation for Security and Co-operation in Europe had been set to meet in Minsk, Belarus, to discuss firming up a ceasefire to be monitored by the OSCE.

Rebel envoy Denis Pushilin, speaking in Minsk, blamed Ukrainians for the worsening security situation and said Kiev should have dispatched envoys capable of taking decisions to the talks. Former Ukrainian president Leonid Kuchma has represented his country at previous negotiation rounds but declined to participate on this occasion.

Residential areas in Donetsk remain caught in the artillery crossfire. Separatist authorities in Donetsk said four people died in a fire yesterday after a warehouse was hit by a shell.

The UN estimates that more than 4,700 people have been killed in eastern Ukraine since April, and fighting has continued despite September's ceasefire deal that included a provision to pull back heavy weapons.

A demarcation line, also agreed in the previous deal signed in Minsk, has been routinely flouted. The US Embassy in Ukraine today accused the rebels of violating the boundary.

"The separatists have pushed their lines well beyond the territorial lines agreed upon," ambassador Geoffrey Pyatt said.

Government officials and rebels have reported fighting along a front extending more than 220 miles.

A fresh truce was announced in December only to unravel last week and derail a planned meeting of the leaders of Ukraine, Russia, France and Germany in Kazakhstan this week.

Ukraine says separatist forces are accumulating along the front line.

Military spokesman Andriy Lysenko said rebels have mobilised large numbers of armoured vehicles in the past few days, with a particular concentration noted in Horlivka, a city east of Donetsk.

"In Horlivka, there is a three-kilometre-long column of tanks heading in the direction of Ukrainian positions," he said.