Ukraine said its troops had taken more territory from pro-Russian rebels near the site where Malaysian flight MH17 was brought down, as international investigators said fighting was preventing them reaching the crash location.
Ukrainian officials said two rebel-held towns had been recaptured and attempts were being made to take a village Kiev says was near the launch site of the surface-to-air missile that shot down the airliner with loss of all 298 on board.
Analysis of black box flight recorders from the airliner showed it was destroyed by shrapnel from a missile blast which caused a "massive explosive decompression", a Ukrainian official said on Monday.
Investigators in Britain, who downloaded the data, had no comment. They said they had passed information to the international crash investigation led by the Netherlands, whose nationals accounted for two-thirds of the victims.
In a report on three months of fighting between government forces and separatist rebels who have set up pro-Russian "republics" in the east, the United Nations said more than 1,100 people had been killed.
U.N. High Commissioner for Human Rights Navi Pillay said increasingly intense fighting in the Donetsk and Luhansk regions was extremely alarming and the shooting down of the Malaysian airliner on July 17 may amount to a war crime.
Western leaders say rebels almost certainly shot the airliner down by mistake with a Russian-supplied surface-to-air missile. Russia accuses Kiev of responsibility.
The separatists are still in control of the area where the plane was shot down but fighting in the surrounding countryside has been heavy as government forces try to drive them out.
On Monday at least three civilians were reported killed in overnight fighting, and Kiev said its troops recaptured Savur Mogila, a strategic piece of high ground about 30 km (20 miles) from where the Malaysia Airlines Boeing hit the ground, and other areas under rebel control.
A spokesman for Ukraine's Security Council, Andriy Lysenko, said Kiev was trying to close in on the crash site and force the rebels out of the area but was not conducting military operations in the immediate vicinity.
He said Ukrainian troops were in the towns of Torez and Shakhtarsk, both formerly held by the rebels, while fighting was in progress for the village of Snezhnoye - close to the presumed missile launch site - and Pervomaisk.
Government troops were also readying an assault on Gorlovka, a rebel stronghold north of the provincial capital Donetsk.
"The Ukrainian military is conducting an