Black box data from the downed Malaysia Airlines plane reveals the jet crashed due to a "massive explosive decompression" after being hit by shrapnel from a missile, claims a Ukrainian security official.
Andriy Lysenko, a spokesman for Ukraine's Security Council, said the information came from experts analysing the flight recorders from MH17, which was shot down over eastern Ukraine killing all 298 people on board.
Air accident experts in Farnborough, Hampshire, had been tasked with downloading the data from the two black boxes and passing the information on to international investigators.
Dutch and Australian police have again been forced back from the crash site
Western countries blame rebels for shooting down the airliner with a missile, mistaking it for a Ukrainian plane, but the separatists deny any involvement.
Meanwhile, a team of Dutch and Australian police making a fresh attempt to reach the crash site were again forced to turn back after "explosions" in the area.
A previous attempt had also been halted by fierce fighting.
Ukraine rebels say they have lost control over part of the MH17 crash site in the face of a push by government forces.
Australia's Deputy Commissioner of National Security Andrew Colvin said evidence risked being lost amid the continuing clashes, and the chances of finding the remains of all the dead grew slimmer as time went on.
The UN's Navi Pillay is demanding a full inquiry into the plane attack
The claims about data from the flight recorders came as the UN said the shooting down of the airliner may amount to a war crime.
The UN High Commissioner for Human Rights Navi Pillay condemned the "horrendous shooting down" of flight MH17, en route from Amsterdam to Kuala Lumpur, and demanded a "thorough, effective, independent and impartial investigation".
She said in a statement: "This violation of international law, given the prevailing circumstances, may amount to a war crime.
Some 100,000 people have fled the violence in eastern Ukraine, says the UN
"Every effort will be made to ensure that anyone committing serious violations of international law including war crimes will be brought to justice, no matter who they are."
Plans have been unveiled to stage a special memorial concert for victims of MH17 in Amsterdam this September.
The Prime Minister David Cameron is due to meet families of British victims at Downing Street on Tuesday.
The UN also said latest figures showed more than 1,100 people had been killed and nearly 3,500 wounded in fighting in eastern Ukraine since April, with both sides using heavy weapons in built-up areas, including artillery, tanks, rockets and missiles.
"Both sides must take great care to prevent more civilians from being killed or injured," Ms Pillay said.
Casualty numbers are rising with the use of heavy weapons in built-up areas
A further 100,000 people have fled the violence.
The UN report also accused the rebels of conducting a brutal "reign of intimidation and terror" in the areas they controlled, including the abduction, torture and killing of civilians.
The US has released satellite images it claims show rockets have been fired at Ukraine from within Russia.
The images, which come from the US Director of National Intelligence and have not been independently verified, also purport to show that heavy artillery for pro-Russian separatists has crossed the border.
Their release appears to be a part of Barack Obama's push to hold Russia accountable for its activities in Ukraine - and persuade European allies to apply harsher sanctions on Moscow.
Moscow has denied allegations of involvement in eastern Ukraine, claiming the US is conducting "an unrelenting campaign of slander against Russia, ever more relying on open lies".
The French presidency later said it would take further measures against Moscow - along with Britain, the US, Germany and Italy - over the situation in Ukraine.