DONETSK, Ukraine (AFP) - Ukrainian forces and pro-Kremlin insurgents said on Friday they have swopped dozens of prisoners under the terms of a fragile truce aimed at ending the five-month eastern revolt.

Separatist leader Andrei Purgin said 31 guerrillas were swopped overnight for 36 Ukrainian soldiers in a town north of the rebel stronghold of Donetsk. "I hope the process will continue further and there will be fewer problems from the Ukrainian side, as well as ours," said Mr Purgin, deputy prime minister in the self-declared Donetsk People's Republic.

"It is going very slowly," he told reporters. "The Ukrainian army has a red list and there are some people they do not want to give back."

In total, he said about 300 prisoners had been exchanged in Donetsk since the ceasefire - 150 from each side, but gave no figures for the neighbouring separatist region of Lugansk.

Ukrainian President Petro Poroshenko said on Twitter that the rebels had released 57 servicemen since Thursday.

He said the ceasefire signed in the Belarussian capital Minsk a week ago gives Kiev a chance "to free our guys, strengthen the army, build a powerful line of defence and protect cities and villages".

The Ukrainian leader had said earlier this week that insurgents had released nearly 650 servicemen out of a total of around 1,200 captured since fighting started in April.

The 12-point Minsk agreement paves the way for negotiations on limited autonomy for parts of the two Russian-speaking regions within a unified Ukraine but some top rebel commanders have vowed to demand outright independence.