Security officials in Ukraine believe the downed Malaysia Airlines jet in eastern Ukraine suffered an explosive loss of pressure after it was punctured by shrapnel from a missile.
They said the information came from the plane's flight data recorders, which were being analysed by British experts.
However, it remains unclear who fired a missile, with pro-Russia rebels and Ukraine blaming each other, according to the BBC.
Many of the 298 people killed on board flight MH17 were from the Netherlands and Dutch investigators leading the inquiry into the crash have refused to comment on the Ukrainian claims.
Meanwhile heavy fighting has prevented an international police force composed of Dutch and Australian officers from reaching the crash site for a second consecutive day.
Ukraine's army said on Monday it had managed to capture two towns near the wreckage in its bid to win back territory from the hands of the rebels.
The international delegation was stopped in Shakhtarsk, a town some 30km away from the area where flight MH17 was brought down.
The town was reportedly struck by shelling, causing residents to flee in cars.
"We are sick and tired of being interrupted by gunfights, despite the fact that we have agreed that there should be a ceasefire," said Alexander Hug, the deputy head of the Organization for Security and Cooperation in Europe (OSCE) team in Ukraine.
They had hoped to secure the site so that the wreckage and human remains could be examined by international crash experts. The BBC reported that most of the bodies have been removed, many of them repatriated to the Netherlands.
Ukrainian security spokesman Andrei Lysenko told reporters on Monday that the plane suffered "massive explosive decompression" after it was hit by fragments he said came from a missile.
Joint investigation launched
New Zealand has agreed to a joint criminal investigation of the shooting down of the airliner. Two New Zealanders were among the dead.
12 countries that lost citizens in the incident have agreed to launch the investigation, which will be carried out by the European judicial cooperation agency - Eurojust.
Eurojust said the venue of a prosecution, if there was one, as well as the applicable law, would be determined by what the investigation found.