Data from recovered flight recorders shows that Malaysia Airlines Flight MH17 crashed in eastern Ukraine because of an explosive loss of pressure after being punctured multiple times by shrapnel, a Ukrainian security spokesman says.

Andrei Lysenko said on Monday the plane suffered "massive explosive decompression" after it was hit by fragments he said came from a missile.

The data recorders were sent to experts in Britain for examination.

The data was released as heavy fighting flared around the debris field, once again preventing an international police team charged with securing the site from even getting there.

Government troops stepped up their push to win back territory from pro-Russian separatists in fighting that the United Nations said on Monday had killed more than 1,100 people in four months.

The international delegation of Australian and Dutch police and forensic experts stopped on Monday in Shakhtarsk, a town around 30km from the fields where the Boeing 777 was brought down.

The unarmed police team's mandate is to secure the currently rebel-controlled area so that comprehensive investigations can begin and any remaining bodies can be recovered.

The Ukrainian Defence Ministry said Ukrainian troops had entered Shakhtarsk, although checkpoints blocking the western entrance into town remained under rebel control. The ministry also said fighting was taking place in Snizhne, directly south of the crash site, and in other towns in the east.

Ukraine has accused rebels of tampering with evidence at the crash site and trying to cover up their alleged role in bringing the Malaysia Airlines jet down with an anti-aircraft missile.

Separatist officials have staunchly denied responsibility for shooting down the airliner and killing all 298 people onboard.

Satellite images

Meanwhile, the US State Department on Sunday released satellite images that it said backed up its claims that rockets had been fired from Russia into eastern Ukraine and that heavy artillery for separatists had crossed the border.

A four-page document released by the State Department purported to show blast marks from where rockets were launched and craters where they landed.

Officials said the images, sourced from the US Director of National Intelligence, showed heavy weapons fired between July 21 and July 26 - after the July 17 shooting down of MH17.

Igor Konashenkov, a spokesman for Russia's defence ministry, on Monday dismissed the images as fake. He said in a statement carried by the Russian news agencies that the images could not serve as proof because they lacked precise locations and their resolution was too low.