Donetsk insurgent leader Alexander Borodai said on Sunday that insurgents have found what are believed to be the flight data recorders of a crashed Malaysian airliner.

"Technical components of the airliner which look like black boxes were discovered in the crash area. They are in Donetsk now and will be handed over to international experts once they arrive," Borodai, prime minister of the Donetsk People's Republic, told reporters.

The objects could not be handed over to representatives of the Ukrainian authorities in case of any falsified examination results, he added.

Meanwhile, a spokesman for the self-proclaimed republic also confirmed the discovery. "They are in an externally intact condition," the spokesman said in an interview with Russia's Life News TV channel.

The insurgent republic had no aviation equipment specialists and could not verify that the devices found at the crash site were black boxes of the wrecked airliner, according to the spokesman.

He reiterated that the insurgent authorities in Donetsk would transfer the devices only to representatives of the International Civil Aviation Organization.

Earlier in the day, insurgents said that black boxes of the crashed Malaysian flight MH17 had been found and brought to Donetsk in eastern Ukraine.

The insurgents said on a Twitter account that "black boxes had been brought to Donetsk," according to the Interfax news agency.

Borodai promised on Saturday that black boxes of the ill-fated Malaysian airliner, if found, would be handed over to international experts.

The Boeing 777 passenger plane of the Malaysia Airlines crashed in eastern Ukraine en route from Amsterdam to Kuala Lumpur on Thursday, killing all 298 people aboard.