The families of those who perished in flight MH17 fear that pro-Russian rebels may keep the bodies as a "bargaining chip".
Pro-Russian separatists have taken control of the crash site in eastern Ukraine and loaded the remains of almost 200 victims on to a train, to be taken to an unknown destination.
There were reports that the rebels, some drunk, forced emergency workers to hand over the bodies at gunpoint as well as claims that the corpses were being looted.
Relatives described the situation as "horrific" and called on Western leaders to do more to ensure the bodies of their loved ones are returned.
International investigators have still not been given free access to the site four days after the Malaysia Airlines jet came down killing all 298 people on board.
Another 21 bodies have been found in the sprawling fields where the plane came down.
Local rescue workers piled 21 black body bags by the side of the road in Hrabove but it was unclear how quickly they would be transported to refrigerated railcars in the nearby town of Torez, where the other bodies are being held.
Ukraine's emergency services agency say the total number of bodies found was 251.
International indignation over the incident has grown as investigators still only have limited access to the crash site and it remains unclear when and where the victims' bodies will be transported.
Pro-Moscow rebels piled nearly 200 bodies from the downed Malaysian jetliner into four refrigerated boxcars and cranes at the crash scene moved big chunks of the Boeing 777, drawing condemnation that the site was being tampered with.
The pressure has been growing on Russian President Vladimir Putin, who the U.S. and others say has backed and armed the rebels, to rein in the insurgents in Ukraine and allow a full-scale investigation.
In other developments:
l Rebels said they had recovered the plane's black box recorders, reportedly on Moscow's orders, as Britain called for them to be returned;
l John Kerry, the US Secretary of State, said it was "pretty clear" that the suspected weapons system behind the attack had been "transferred from Russia" to the hands of separatists;
l Memorial services in honour of the dead were held around the world.
Reports that the bodies of the 298 victims have been left at the mercy of looters, have also attracted international condemnation.
Hugo Hoare, whose brother Andrew died, said: "What the hell is going on? The fact that the rebels have taken the bodies concerns me. Are they taking care of them? What are they going to do with them?
"I just hope whatever they are doing is humane and their intention is just to release them at the appropriate time. The first thing I thought was what if they are going to use them as a bargaining chip?
Asked if he feared the rebels may try to use the bodies to their advantage, Barry Sweeney, whose son Liam died, said: "It is a concern. It is a situation I am trying not to think about."
He added: "All I want for me and all the families is for the 298 people to come home. These are 298 innocent people who have died and my request to the Government is for them to do what they can to sort this out.
"Not enough is being done. It should have happened straight away. Everyone needs to stop being idiots and bring these people home so they can be laid to rest."
Jordan Withers, nephew of victim Glenn Thomas, said: "It's becoming more apparent from what we have seen or heard that there is growing concern about decomposing bodies at the scene and about looters.
"That is a real concern of ours. My uncle had personal belongings with him on the plane that his partner and us would like to get back.
"Our main concern and priority is getting his body back so that we can have some sort of closure and say our goodbyes."
He said the family feared they may have to have a "symbolic funeral" rather than an actual one. "We just hope the situation is resolved quickly and peacefully, but the longer it is the less likely that seems. And less likely we will get him home."
Putin criticised the Ukraine authorities in Kiev for reigniting the fighting with the pro-Russian rebels who control the crash site.
"We can say with confidence that if fighting in eastern Ukraine had not been renewed on June 28, this tragedy would not have happened," Putin said. "Nobody should or does have a right to use this tragedy for such mercenary objectives."