Heavy shelling around the crash site of downed Malaysian flight MH17 forced Dutch and Australian police to scrap a planned trip on Sunday, as 13 people including two children were killed during clashes in insurgent-held east Ukraine.
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.
But international observers overseeing the trip had to abruptly ditch their plans 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.
"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, the biggest city in the region.
An AFP photographer heard artillery bombardments just a kilometre (half a mile) from the rebel-held town of Grabove next to the crash site and saw black smoke billowing 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.
- 'It's the insurgents' -
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.
"I hope that this agreement... will ensure security on the ground, so the international investigators can conduct their work," Razak said, adding that 68 Malaysian police personnel would leave Kuala Lumpur for the crash site on Wednesday.
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 by both the Kiev forces and pro-Russian separatists.
Fighting was raging elsewhere as the Ukrainian army pushes on with its offensive to retake the vital industrial east.
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 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.
- Brussels mulls more sanctions -
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.
Sanctions targeting economic sectors including an arms embargo are being considered, while on Tuesday the bloc is expected to unveil more names of individuals and entities sanctioned.
Moscow has blasted the move as "irresponsible", and warned that it jeopardised cooperation on security issues.
Meanwhile in Kiev, lawmakers are to meet next week to discuss Prime Minister Arseniy Yatsenyuk's future, after the premier quit in fury over the collapse of his coalition.
About 1,000 people -- including the victims of the Malaysian plane crash -- have been killed in the deadly insurgency, and the United Nations estimates that some 230,000 have fled their homes.
The Red Cross has said the country is now in civil war -- a classification that would make parties in the conflict liable to prosecution for war crimes.