Dutch forensics experts have identified 21 more victims of flight MH17, the government said on Friday, while their colleagues at the crash site began arriving home from east Ukraine where fighting has stopped the investigation.

Only two bodies had previously been identified. The 21 new victims are made up of 16 Dutch, including a dual British national, two Malaysians, a German, a Canadian and a Briton, the Dutch justice ministry said in a statement.

The prime minister of Ukraine's self-proclaimed Donetsk People's Republic announced Thursday that he was resigning his position.

Russian citizen Alexander Borodai said he was stepping down in favor of a local field commander, Alexander Zakharchenko, after finishing his work as a "start-upper".

NATO chief Anders Fogh Rasmussen urged Russia to "step back from the brink" during a visit to Kiev on Thursday and vowed support for Ukraine as fears mounted that Moscow was preparing to send troops into the conflict-torn east of the country.

His visit came as the center of the main rebel bastion Donetsk was hit by sustained bombardment for the first time in four months of fighting, and a dozen civilians were killed around the region.

Seven employees of a fitness center huddled in its basement in the heart of rebel-held Donetsk on Thursday as the center of the besieged city came under sustained shelling for first time.

Above them a mortar had torn a gaping hole in a wall of the spa complex, smashing all of the windows.

Thick smoke from burning tires once again billowed into the blue sky over Kiev's iconic Independence Square on Thursday as a rump of demonstrators still living in the protest camp scuffled with authorities trying to clear the area.

Dozens of demonstrators hurled stones and set debris alight as they halted a short-lived push by municipal workers backed by interior ministry troops to dismantle barricades around the entrance to the central square with bulldozers.

Russia retaliated against tough new Western sanctions on Thursday, banning most food imports from the United States and the European Union and threatening to block flights over its airspace.

The 28-member European Union swiftly denounced the measures -- which also target Canada and Australia -- and said it was ready to take action in response.

One person was killed and two injured Thursday when a hospital in the center of the besieged rebel stronghold of Donetsk in eastern Ukraine was hit by shelling, local health authorities said.

"Today as a result of a mortar shell hitting the... first Donetsk city hospital, one person died and two were injured," the regional health administration said in a statement, adding that no medics were among the casualties.

Flags flew at half mast Thursday as Australia held a national day of mourning for those killed in the MH17 crash in Ukraine, a day after experts suspended the search for body parts.

Australia lost 38 citizens and residents, including children, when the Malaysia Airlines plane from Amsterdam to Kuala Lumpur was shot down over eastern Ukraine on July 17, killing all 298 on board.

NATO Secretary General Anders Fogh Rasmussen will visit Kiev Thursday, Ukraine's foreign ministry said, amid heightened tensions over allegations Russia is massing troops along its ex-Soviet neighbor's border.

The visit, at the invitation of Ukrainian President Petro Poroshenko, is intended to discuss an upcoming meeting on NATO-Ukraine partnership, the foreign ministry said Wednesday.

Dutch, Australian and Malaysian investigators at the eastern Ukraine crash site of downed flight MH17 are enlisting the help of local villagers in finding victims' remains and possessions, the Dutch justice ministry said on Wednesday.

"Residents are being asked to locate remains and personal belongings. They are also being given the opportunity to tell what they saw or experienced during the disaster," the ministry said in a statement issued in The Hague.