The deal on Monday was for a 60-man convoy to approach the site under rebel escort and then to be handed over to a Ukrainian army escort to complete the 100-kilometre journey. But it fell through as the town of Shakhtersk, 12 kilometres short of the crash site, came under heavy bombardment – forcing the investigators to retreat to their city hotel.

As they headed through the last rebel checkpoint on the western approach to the town, civilians fled in the opposite direction – some of them bidding for safe passage with makeshift notices announcing that children were on board.

As another nine AFP members arrived in Donetsk, bringing their number to 20, the Organisation for Security and Co-operation in Europe, which facilitates the investigators’ travel to the site, vented its frustration after being blocked from the site for four straight days.

“It’s unconscionable that human remains are out there still – we have seen them and geo-located some of them,” OSCE spokesman Michael Bociurkiw said. “And we know there’s more to be found.”

Alluding to a Dutch estimate that as many as 100 bodies are still to be recovered, the deputy chief of the OSCE mission, Alexander Hug, added: “The longer that these body parts remain out there, the greater is the risk that they will disappear.”

Officials in Kiev have not publicly explained why they are pressing their attack on the rebels in the Donetsk and Luhansk regions at a time when foreign access to the crash site is so vital, but a spokesman for the Ukrainian Security Council, Andriy Lysenko, claimed that Kiev was trying to force rebels out of the crash site without conducting military operations in the immediate area.

The distressing reality for grieving families in the West is that differing cultural sensitivities and combat imperatives have kicked in – both sides in this full-blown separatist war have been hardened by the loss of hundreds of their own and the crash site is strategically placed in relation to towns, including Donetsk, the capture of which will dictate the outcome of the war.

Donetsk has become a ghost town as people flee or remain indoors amid widespread speculation that an all-out Ukrainian assault on what is the seat of separatist power is imminent.

Evenings are punctuated by the regular rumble of not-so-distant explosions and local officials say that residential areas, power lines and a gas pipeline have been damaged.

On the outskirts of the city, at Petrovskiy, on Monday, Fairfax Media encountered residents preparing a bomb shelter and a grief stricken Dimitriy Gorozhaninov, who was mourning four members of his family. Mr Gorozhaninov said his family died in a Ukrainian artillery barrage in the days before a missile strike caused flight MH17 to crash with the loss of 298 passengers and crew – 38 of whom were Australian.

Refusing to blame either side for the collapse of Monday’s access deal, Mr Hug said: “We had to return for security reasons when all parties involved knew our route, knew who was in the convoy and the precise location we were trying to get to – there were no surprises.

“There was fighting on the road when all sides knew we would be on the road, but we remain determined ... the issue is that there are human remains out there and the families and their governments want them back.”

Asked which side controlled the site, which had been under rebel control since the July 17 crash, Mr Hug said that the control had become fluid – “it can change in two hours”.

As the Ukrainian army and the rebels hammered each other, another complication arose – quite apart from control of the 50-square-kilometre site.

The crash investigators need to open a corridor to the town of Torez, about 15 kilometres away, to load the plane’s wreckage for shipment to a safe location where it can be studied.

The rebels have already taken it upon themselves to load a train with a small portion of passengers’ possessions that are strewn across the rolling hills. The train is at a platform in the Torez railway station, but has yet to be formally handed over to the investigators.

Rebel spokesmen conceded that they had lost control of some of the crash site, but denied that the Kiev forces had taken the towns of Torez and Shakhtersk or that Snezhnoye and Pervomaisk were about to slip from their grip. But it seemed that the Ukrainian army had snatched the strategic high ground around Savur-Mohyla, on the border of the Donetsk and Luhansk regions.