Heavy shelling around the crash site of downed Malaysian flight MH17 has forced Dutch and Australian police to scrap another planned trip to ground zero.

The unarmed contingent of law enforcement officers were due to head to the location 10 days after the disaster following a deal with rebels aimed at allowing a long-delayed probe to go ahead.

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But international observers overseeing the trip had to abruptly ditch their plans on Sunday after clashes shattered a supposed truce between government forces and insurgents in the area around the site, where some remains of the 298 victims still lie decomposing under the summer sun.

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“There is fighting going on. We can’t take the risk,” said Alexander Hug, deputy chief monitor of the European security body OSCE’s special mission in Ukraine.

“The security situation on the way to the site and on the site itself is unacceptable for our unarmed observer mission,” he told reporters in the insurgent stronghold Donetsk.

A pro-Russian separatist mans a checkpoint in Ukraine. Photo: AAP

Artillery bombardments could be heard just a kilometre from the rebel-held town of Grabove next to the crash site as black smoke billowed into the sky.

Terrified local residents were fleeing and checkpoints controlled by separatist fighters were abandoned.

The Dutch justice ministry confirmed that security advisers had also halted a trip by a team of forensic experts.

“Because of fighting in the area, the situation is still too unstable to work at the crash site,” the ministry said in a statement.

Earlier Australian Prime Minister Tony Abbott said 49 officers from the Netherlands and Australia – which together lost some 221 citizens in the crash – were due at the scene Sunday and that there would be “considerably more on site in coming days”.

That came after Malaysian Prime Minister Najib Razak said he had reached an agreement with the pro-Russian insurgents controlling the site to allow the police deployment.

So far investigators have been able to visit the site only sporadically because of security concerns, even though a truce had been called in the immediate area around the site.

Fighting was raging elsewhere as the Ukrainian army pushes on with its offensive to retake the vital industrial east.

Dutch and Australian investigators talk with Ukrainian police. Photo: AAP

Local authorities said 13 people including two children aged one and five were killed on Sunday in heavy fighting in rebel holdout Gorlivka, about 45 kilometres to the north of Donetsk, and which has a population of about a quarter of a million.

Mining hub Donetsk itself was also subject to heavy bombardment throughout the night, some of it apparently unguided Grad rocket fire.

The city of one million has been serving as a base for international monitors and journalists who are travelling daily to the crash site.

Ignoring safety warnings, an Australian couple had travelled to the scene without any escort on Saturday, saying they were fulfilling a promise to their only child that they would be there.

“She was full of life,” said Angela Rudhart-Dyczynski of their 25-year-old daughter Fatima, an aerospace engineering student.

Dutch authorities, who are leading the probe into the downing of the Amsterdam-to-Kuala Lumpur plane, have identified the first victim, after 227 coffins were flown to the Netherlands for identification.

The insurgents have also handed over a sealed train carriage filled with victims’ belongings to the Dutch.

In Brussels, the European Union is drafting tougher sanctions against Russia – which it accuses of abetting the insurgency by arming the rebels who allegedly shot down the aircraft.

UN says plane’s downing may be a war crime

The downing of Malaysia Airlines flight MH17 “may amount to a war crime”, the UN says, adding that fighting in eastern Ukraine has claimed more than 1100 lives with both government and rebel forces using heavy weaponry in built-up areas.

UN High Commissioner for Human Rights Navi Pillay condemned the “horrendous shooting down” of the Malaysian passenger jet in rebel-held territory that killed all 298 people on board, and demanded a “thorough, effective, independent and impartial investigation”.

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“This violation of international law, given the prevailing circumstances, may amount to a war crime,” she said in a statement.

“Every effort will be made to ensure that anyone committing serious violations of international law including war crimes will be brought to justice, no matter who they are,” Pillay said.

Part of the MH17 wreckage. Photo: Getty

Pillay described reports of increasingly intense fighting in rebel bastions Donetsk and Lugansk regions as “extremely alarming” and said both sides were “employing heavy weaponry in built-up areas, including artillery, tanks, rockets and missiles”.

About 100,000 people have now fled the conflict zone in the east for other areas of Ukraine, the UN said in the report released on Monday.

The report also accused rebels controlling swathes of territory of conducting a brutal “reign of terror” in the areas they control, including the abduction, torture and killing of civilians as the rule of law has collapsed.

“These groups have taken control of Ukrainian territory and inflicted on the populations a reign of intimidation and terror to maintain their position of control,” the report said.

– AAP