US Secretary of State John Kerry has laid out what he called overwhelming evidence of Russian complicity in the downing of Malaysia Airlines flight MH17 and called pro-Russian separatists' behaviour "grotesque".

Mr Kerry expressed horror at how pro-Russian separatists at the crash sites in eastern Ukraine treated the remains of victims from Thursday's disaster, criticised Russian President Vladimir Putin, and threatened "additional steps" against Moscow.

"Drunken separatists have been piling bodies into trucks and removing them from the site," Mr Kerry said on NBC television.

"What's happening is really grotesque and it is contrary to everything President Putin and Russia said they would do."

British Foreign Secretary Philip Hammond echoed the criticism, urging Moscow to ensure international investigators had access to the crash sites.

"Russia risks becoming a pariah state if it does not behave properly," he told Sky television.

At the biggest crash site, where emergency workers had bagged dozens of bodies on Saturday, all had been removed on Sunday morning.

Bloodstained military stretchers that had carried them lay empty by the road, and rescue workers used a crane to move wreckage to reach human remains trapped beneath.

As Ukraine accused the rebels of hiding evidence relating to the shooting down of the airliner with the loss of 298 lives, a pro-Russian separatist leader said items thought to be the stricken Boeing's "black boxes" were now in rebel hands.

With Western anger rising at the apparently disrespectful treatment of the bodies by the rebels controlling the widely spread crash sites, nearly 200 corpses were taken to be stored on a refrigerated train at Torez, 15km away.

"It's corpses. They brought the bodies overnight," a duty officer at the town's station told Reuters.

Officials from the Organization of Security and Cooperation in Europe were able to inspect some railway wagons.

Russia denies any involvement in shooting down the airliner and has blamed the Ukrainian military.

While stopping short of direct blame on Moscow, Mr Kerry put forward the most detailed US accusations so far that Russia provided the insurgents with the sophisticated anti-aircraft systems used to down the aircraft.

The United States had seen supplies moving into Ukraine from Russia in the last month, including a 150-vehicle convoy of armoured personnel carriers, tanks and rocket launchers given to the separatists, he said.

It had also had intercepted conversations about the transfer to separatists of the Russian radar-guided SA-11 missile system which it blames for the Boeing 777's destruction. "It's pretty clear that this is a system that was transferred from Russia," Mr Kerry said in an interview on CNN.

"There's enormous amount of evidence, even more evidence that I just documented, that points to the involvement of Russia in providing these systems, training the people on them," Mr Kerry said on CBS.

While Ukrainian President Petro Poroshenko issued a renewed appeal for backing from the international community, some European nations, with an eye to their trade links with Russia, have been less enthusiastic about confrontation.

Mr Kerry challenged the Europeans to be more assertive. "It would help enormously if some countries in Europe that have been a little reluctant to move would now recognise this wakeup call and join the United States and President Obama in taking the lead, and also stepping up," he said.

The United Nations Security Council was considering a draft resolution to condemn the attack, demand armed groups allow access to the crash sites and call on states in the region to cooperate with an international investigation. It could be put to a vote as early as Monday.

The Netherlands, whose citizens made up two-thirds of the 298 on the flight, said it was "furious" about the manhandling of corpses strewn over open country and asked Ukraine for help to bring "our people" home.

A spokesman for Ukraine's Security Council, Andriy Lysenko, accused the rebels of a cover-up.  "The terrorists are doing everything to hide the evidence of the involvement of Russian missiles in the shooting down of that airliner," he told a news conference in Kiev.

He said the rebels had taken debris and bodies from the crash site in trucks, tampering with a scene that investigators need to be secure to have a chance of determining what and who caused the plane to plunge into the steppe.

A separatist leader said items thought to be the "black box" voice and data recorders from the airliner had been found.

"They are under our control," Aleksander Borodai, prime minister of the self-styled Donetsk People's Republic, told a news conference.