A Malaysian expert (L) examines a black box belonging to Malaysia Airlines flight MH17 during its handover from pro-Russian separatists in Donetsk, on July 22, 2014. [Photo/Agencies]

DONETSK, Ukraine - The remains of some of the nearly 300 victims of the Malaysia Airlines plane downed over Ukraine were making their way to the Netherlands on Tuesday as a senior Ukrainian separatist leader handed over the plane's black boxes to Malaysian experts.

Dutch Prime Minister Mark Rutte told a news conference on Monday that a train carrying around 200 body bags was on its way to rebel-held Donetsk and then to Kharkiv, which is in Ukrainian government hands, from where the bodies would be taken back to the Netherlands to be identified.

The train left the crash site after the Malaysian prime minister reached agreement with the separatists for recovered bodies to be handed over to authorities in the Netherlands, where the largest number of victims came from.

Early on Tuesday, senior separatist leader Aleksander Borodai handed over the black boxes in the city of Donetsk.

"Here they are, the black boxes," Borodai told a room packed with journalists at the headquarters of his self-proclaimed Donetsk People's Republic as an armed rebel placed the boxes on a desk.

Colonel Mohamed Sakri of the Malaysian National Security Council told the meeting the two black boxes were "in good condition".

The handover of the bodies and black boxes, and reports by international investigators of improved access to the wreckage of the airliner four days after it was shot down, occurred against calls for broader sanctions against Russia for its support for the rebellion, although Western leaders are struggling to agree on a united response.

Shaken by the deaths of 298 people from across the world, Western governments have threatened Russia with stiffer penalties for what they say is its backing of pro-Russian militia who, their evidence suggests, shot the plane down.