Ukrainian president Petro Poroshenko on Monday said he had ordered government forces to halt fire in a 40 kilometre (24-mile) area around the crash site of Malaysia Airlines flight MH17.
"I have given an order: immediately within a 40 kilometre radius around the disaster site Ukrainian troops must not conduct operations and must not open fire," Poroshenko was quoted as telling journalists by the Interfax Ukraine news agency.
Ukraine launched a military assault to break pro-Russian rebels' hold on the eastern city of Donetsk on Monday in the first major hostilities in the area since Malaysia Airlines flight MH17 was shot down last week.
As investigators arrived to inspect the bodies of hundreds of victims near the crash site, the fighting in Donetsk served as a reminder of the dangers they face working in a war zone.
Artillery fire sent plumes of smoke skywards near the Donetsk railway station, around 60 km (40 miles) from the crash site, in what the separatists said was an attempt by government forces to enter the city they seized in April.
Sergei Kavtaradze, of the rebels' self-proclaimed Donetsk People's Republic, said at least four army tanks and armoured vehicles were trying to break through into the city. Reuters also saw two rebel tanks heading towards the railway station.
A Ukrainian military spokesman confirmed that the operation was in progress but would not comment on reports of troops entering Donetsk. "The active phase of the anti-terrorist operation is continuing. We are not about to announce any troop movements," Vladyslav Seleznyov said.
Donetsk is at the heart of a rebel uprising against rule by Kiev, and Ukrainian President Petro Poroshenko has vowed to retake the city as part of what Kiev calls its "anti-terrorist operation" against the separatists.
Ukrainian State Emergency Service employees collect bodies of victims at the site of the crash. AFP
Against a background of international horror over the fate of the remains of the 298 victims of the Malaysia Airlines disaster, the first international investigators reached eastern Ukraine on Monday.
Three members of a Dutch disaster victims identification team arrived at a railway station near the crash site where rebels say 247 bodies have been stored in refrigerated wagons.
About one third of the crash victims were Dutch.
The head of the team inspected the storage of the bodies in the rail cars and, despite an overwhelming stench of decomposition when the doors were opened, said it was fine.
"The storage of the bodies is of good quality," said Peter van Vliet, whose team went through the wagons dressed in surgical masks and rubber gloves.
Van Vliet said he had been told the train would be leaving the station at Torez later on Monday so that bodies can be taken to where they can be identified and repatriated. He could not say where it was going.
Ukrainian officials said as of Monday morning 272 bodies and 66 fragments of bodies had been found.
The shooting down of the airliner on Thursday has sharply deepened the Ukrainian crisis, in which separatists in the Russian-speaking east have been fighting government forces since protesters in Kiev forced out a pro-Moscow president and Russia annexed Crimea in March.
The United States and its allies have pointed the finger at the pro-Russian rebels and at Moscow itself over the downing of the plane. Russia has denied involvement and blamed the Ukrainian military for the disaster.
The pro-Western authorities in Kiev accuse the rebel fighters of shooting down the airliner, killing all 298 people on board. The separatists deny they are to blame.
Earlier on Monday, three members of a Dutch Disaster Victims Identification team arrived in Donetsk, hoping to check the remains of some of the victims of the plane crash. A team of Malaysian officials were also due to arrive on Monday. The downing of the airliner has intensified calls for the fighting to end in eastern Ukraine.
Sergei Kavtaradze, an official of the rebels' self-proclaimed Donetsk People's Republic, said there were at least four tanks and armoured vehicles trying to break through into the city.
A spokesman for Ukraine's military operations in eastern Ukraine said the operation was in an "active phase" but could not comment on reports of troops entering Donetsk because he did not want to give away the Ukrainian strategy.
Recording may show attempt at cover-up of downed Malaysian airliner
SHOCK TURNS TO ANGER US
Secretary of State John Kerry laid out what he called overwhelming evidence of Russian complicity in the shooting down of the Malaysia Airlines plane.
Kerry demanded that Moscow take responsibility for actions of pro-Russian rebels in eastern Ukraine whom Washington suspects of downing the jet with a missile, and expressed disgust at their "grotesque" mishandling of the bodies.
Television images of the rebel-controlled crash sites, where the remains of victims had lain decomposing in fields among their personal belongings, have turned initial shock and sorrow after Thursday's disaster into anger.
Members of the Ukrainian Emergencies Ministry gather and place bodies at the crash site of Malaysia Airlines Flight MH17. REUTERS
Emotions ran high in the Netherlands, the home country of about two thirds of the 298 people who died in the Boeing 777. The Dutch foreign minister has said the nation is "furious" to hear bodies were being "dragged around", while relatives and church leaders demanded they be rapidly returned home.
But the departure of dozens of corpses loaded into the refrigerated railway wagons was delayed on Sunday as Ukrainian officials and rebels traded blame over why the train had not yet left the war zone, and where or when international investigators would be able to check it.
The UN Security Council is scheduled to vote on Monday on a resolution that would condemn the downing of the plane, and demands that those responsible be held accountable and that armed groups not compromise the integrity of the crash site.
In an apparent attempt at compromise with Moscow, the wording of the resolution, drafted by Australia, was changed to characterise the incident as the "downing" of the flight, instead of "shooting down", according to the final draft obtained by Reuters. Diplomats said it was unclear if Russia would support the final version.
In Washington, Kerry criticised Russian President Vladimir Putin and threatened "additional steps" against Moscow.
Members of the Ukrainian Emergencies Ministry, medical personnel and a crane operator work at the crash site. REUTERS
"Drunken separatists have been piling bodies into trucks and removing them from the site," he said on NBC television on Sunday. "What's happening is really grotesque and it is contrary to everything President Putin and Russia said they would do."
Russia has blamed the Ukrainian military for the disaster. But while stopping short of directly blaming Moscow, Kerry put forward the most detailed U.S. accusations so far, based on the latest US intelligence assessments.
British Foreign Secretary Philip Hammond urged Moscow to ensure international investigators had access to the crash sites. "Russia risks becoming a pariah state if it does not behave properly," he told Sky television.
Australian Prime Minister Tony Abbott said he had spoken to Putin for the first time about the disaster. At least 27 Australian passengers were on the flight from Amsterdam to Kuala Lumpur.
Abbott said an Australian investigation team was in Kiev but had been unable to travel to the site. He said there had been some improvement with the Ukrainian government offering access.
"But there's still a hell of a long way to go before anyone could be satisfied with the way that site is being treated," Abbott said. "It's more like a garden cleanup than a forensic investigation. This is completely unacceptable."
After lying for two days in the summer heat, the bodies had been removed from much of the crash site by Sunday, leaving only bloodstained military stretchers along the side of the road.
As Ukraine accused the rebels of hiding evidence relating to the loss of the airliner, a separatist leader said items thought to be the stricken jet's "black boxes" were now in rebel hands.
Investigators from the UN aviation agency arrived in Ukraine to help to investigate the crash, but a senior official said safety concerns prevented them from reaching the crash site.
Ukrainian State Emergency Service employees search for bodies amongst the wreckage at the crash site. AFP
Kerry said the United States had seen supplies moving into Ukraine from Russia in the last month, including a 150-vehicle convoy of armoured personnel carriers, tanks and rocket launchers given to the separatists.
It had also intercepted conversations about the transfer to separatists of the Russian radar-guided SA-11 missile system, which it blames for the Boeing 777's destruction. "It's pretty clear that this is a system that was transferred from Russia," Kerry said in an interview on CNN.
Kerry's evidence of a Russian connection tracked closely an official unclassified U.S. intelligence summary released over the weekend. It said intelligence analysts confirmed the authenticity of an audiotape conversation provided to the media by Ukrainian authorities of a known separatist leader boasting of downing the plane.
"We also have information indicating that Russia is providing training to separatist fighters at a facility in southwest Russia" that includes missile systems, it said.
The United States has already imposed sanctions on individuals and businesses close to Putin but Kerry indicated that President Barack Obama might go further. "The president is prepared to take additional steps," he told Fox News, although he ruled out sending in US troops.
European Union ministers should be ready to announce a fresh round of sanctions at a meeting of the EU's Foreign Affairs Council this week, said a statement from British Prime Minister David Cameron's office, issued after telephone calls with French President Francois Hollander and German Chancellor Angela Merkel.