DONETSK, UKRAINE (REUTERS) - A senior separatist leader, Alexander Borodai, handed over black boxes from an airliner downed over eastern Ukraine to Malaysian experts in the city of Donetsk in the early hours of Tuesday.

"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.

Both sides then signed a document, which Borodai said was a protocol to finalise the procedure after lengthy talks with the Malaysians.

"I can see that the black boxes are intact, although a bit damaged. In good condition," Colonel Mohamed Sakri of Malaysian National Security Council said in extending his thanks to "His Excellency Mr.Borodai" for passing on the recorders.

Borodai also said a train carrying the remains of the victims of the Malaysia Airlines plane catastrophe has reached Donetsk. It is on its way to Kharkiv, some 300km north-west. The Malaysian experts and a Dutch delegation also on site in Donetsk will travel along with it, he said.