Ukrainian Defence Minister Valeriy Heletey warned on Sunday night that his country could restart its own nuclear programme.

The minister said that the programme would be revived if Kiev does not receive satisfactory military support against what he alleged was a nuclear threat from Russia.

“If we fail to defend Ukraine today, if the world does not help us, we will have to get back to the creation of such weapons which will defend us from Russia,” he threatened.

Mr Heletey stressed that his country sought military support from Nato, the United States and Britain in particular.

And he claimed that his country was already receiving arms from Nato.

Those claims were repeated by another senior official but were later denied by four of the five Nato countries he mentioned.

Meanwhile, government troops resumed shelling rebel-held Donetsk.

Shelling killed six people and wounded 15 others in the city, its council reported yesterday — the worst violation yet of the ceasefire that took effect on September 5.

The city had been heavily shelled on Sunday, damaging both residential and administrative buildings, the council said.

Observers from the Organisation for Security and Co-operation in Europe said that they had been only 650 feet away from where four shells burst in the embattled city. 

Nevertheless, prisoner exchanges continued despite the hostilities and another 73 Ukrainian soldiers were freed late on Sunday night in an exchange with the rebels. 

Donetsk rebel leader Andrei Purgin confirmed that 73 rebels had been released in return.