A train laden with bodies salvaged from the wreckage of the Malaysia Airlines flight MH17 is being held up by "terrorists", the Ukranian government has disclosed.

In a statement on Monday morning, the government said the train, carrying the remains of 200 victims, is being held up in the town of Torez.

Rescuers have found 251 bodies of the 298 victims in the area near the Ukraine-Russia border where the Malaysia Airlines flight came down on Thursday. Some 86 body parts have also been recovered.

The train, believed to be held up by pro-Russian seperatists, comes despite comments from Russian President Vladimir Putin that "we need to do everything to ensure the security and safety of the observers and the experts working at the crash site".

The final destination of the train is not yet known.

Fighting has also been reported in the area surrounding Torez, with reports of four government and two rebel tanks heading to the station.

Politicians, investigators and relatives of the dead have expressed anger over the weekend at the salvage operation, dubbed by some as a "farce". The Russian government has yet to force pro-Russian rebels, who control the crash site area in eastern Ukraine, to cooperate with rescue and recovery teams, and there has yet to be any forensic examination of the crash site.

The UN security countil is due to vote on Monday on a resolution demanding armed groups do not compromise the integrity of the crash site.

But experts from the Organisation for Security and Co-operation in Europe (OSCE) told The Guardian that vital clues about how the Malaysia Airlines Boeing 777 was brought down could be lost forever as the site, which spans 10km of green fields, continues to be a "free-for-all" days after the tragedy.