KIEV forces moved towards the heart of rebel territory in Ukraine today, fighting their way towards Donetsk in an attempt to dislodge pro-Russian fighters.

Separatist leader Sergei Kavtaradze said Ukrainian government forces were trying to break into Donetsk and fighting was under way near the city’s railway station.

Mr Kavtaradze, of the self-proclaimed Donetsk People’s Republic, said that at least four tanks and armoured vehicles were attacking his forces.

A Kiev military spokesman admitted that the operation was in progress but refused to comment on troop movements.

Donetsk is about 50 miles from the crash site of the downed MH17 airliner and fighting in the area was said to be hampering attempts to investigate.

Meanwhile, both Russia and Kiev exchanged accusations about the shooting down.

The Russian Defence Ministry claimed that a Ukrainian military plane flew within three miles of of flight MH17 just before the crash.

The ministry said it detected a Ukrainian SU-25 combat jet on radar and noticed an increase in radar activity just before the Malaysian Airlines plane carrying 298 people was destroyed.

The airliner veered off course above Donetsk and the reason will only be learned from its flight data recorders, the Kremlin said.

It also claimed Ukrainian air defence forces had three or four BUK-M1 systems on combat duty on the day of the crash.

Ukraine’s Prime Minister Arseniy Yatsenyuk counter-charged that Russia had a clear role in shooting down the airliner.

He insisted that the Boeing 777 was probably brought down by a BUK-M1 missile launcher.

“This system could not be operated by drunk pro-Russian terrorists. There were professional people,” he claimed.

And reactionary Australian Prime Minister Tony Abbott demanded that control of the crash site should be handed over to independent experts, saying: “This is still an absolutely shambolic situation. It looks more like a garden clean-up than a forensic investigation.

“Given the almost certain culpability of the Russian-backed rebels in the downing of the aircraft, having these people in control of the site is a little like leaving criminals in control of a crime scene.”