Heavy fighting raged Monday around the Malaysia Airlines debris field, once again preventing an international police team charged with securing the site from even getting there.
Government troops have stepped up their push to win back territory from pro-Russian separatists in fighting that the United Nations said Monday has killed more than 1,100 people in four months.
The international delegation of Australian and Dutch police and forensic experts stopped Monday in Shakhtarsk, a town around 20 miles (30 kilometres) from the fields where the Boeing 777 was brought down.
Sounds of regular shelling could be heard from Shakhtarsk and residents were seen fleeing town in cars.
Associated Press reporters saw a high-rise apartment block in Shakhtarsk being hit by at least two rounds of artillery.
The mandate of the police team is to secure the currently rebel-controlled area so that comprehensive investigations can begin and any remaining bodies can be recovered.
Their visit was cancelled Sunday amid safety concerns.
The Defence Ministry says Ukrainian troops have entered Shakhtarsk, although checkpoints blocking the western entrance into town remain under rebel control. It also said fighting was taking place in Snizhne, which lies directly south of the crash site, and in other towns in the east.
Ukraine has accused rebels of tampering with evidence at the plane 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.
A Ukrainian security spokesman said Monday that data from the recovered flight recorders shows Malaysia Airlines Flight 17 crashed due to a massive, explosive loss of pressure after being punctured multiple times by shrapnel. Andrei Lysenko said 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.