DONETSK Ukraine (Reuters) - A rebel leader appealed to Russia on Saturday for help with worsening conditions at the crash site of a Malaysian airliner, accusing the Ukrainian government of preventing experts from arriving and allowing bodies to rot.

Aleksander Borodai, prime minister of the self-styled Donetsk People's Republic, said rebels had not touched the site where the plane crashed, killing all 298 people on board, but were worried by the state of bodies spread over a large area.

"There's a grandmother. A body landed right in her bed. She says 'please take this body away'. But we cannot tamper with the site," he told a news conference.

"Bodies of innocent people are lying out in the heat. We reserve the right, if the delay continues ... to begin the process of taking away the bodies. We ask the Russian Federation to help us with this problem and send their experts," he said.

He blamed the authorities in the Ukrainian capital Kiev for preventing experts from getting to the site, which is in rebel hands. Earlier on Saturday, Malaysian experts arrived in Kiev to help Ukrainian specialists at the site.

Workers from Ukraine's Emergencies Ministry have been working in the fields where the plane crashed, but monitors from the Organization for Security and Cooperation in Europe (OSCE) have been barred from parts of the site by armed men.

Borodai said the OSCE, a security watchdog, was there to monitor the work of the experts, so for the time being had little to do until those specialists arrived.

"Maybe this is because Ukraine or the Ukrainian authorities are not interested in an objective investigation," he said.

Investigators are keen to establish the whereabouts of the plane's black box flight recorders, but Borodai, just as several other officials have done, said he did not know where they were.

"The black boxes have not been found and we are not touching the site," he said.

(Reporting by Peter Graff; Writing by Elizabeth Piper; Editing by Louise Ireland)