Donetsk: The war and the Australians have come to Donetsk. As the town empties, forces loyal to the central government in Kiev on Sunday stepped up a ferocious new round of attacks on separatist rebels – forcing Canberra’s first substantive MH17 investigative team to abort what would have been its first day at the sprawling crash site.

As evening fell, the rumble of not-so-distant artillery and volleys of gunfire reverberated through Donetsk and a huge curtain of smoke hung in the northern sky.

Kiev’s stepped-up assaults on rebel positions seem as much a campaign to retake rebel-controlled villages and towns as an effort to seize control of the sprawling crash site, on which foreign forensic teams are desperate to gather the remains of as many as 100 crash victims and the personal possessions of all 298 passengers and crew – 38 of them Australian.

After offering a combat-free zone within 40 kilometres of the crash site, the Ukraine government has not explained its military push into the region north and east of this rebel-held provincial centre, save for a declaration that the fall of Horlivka, just 40 kilometres to the north, was imminent and that, Kiev insists, will pave the way for a major assault on Donetsk, one of two remaining rebel strongholds.

On Sunday, there were clashes at Shakhtersk, just 12 kilometres from the crash site, after reports that a column of Ukrainian Army tanks and armoured personnel carriers had entered the town; at Torez, 15 kilometres away, and the town from which the bodies of the MH17 victims were dispatched by rail as the first stage in their repatriation to home countries; and at Snizhne, the town from which a Russian-sponsored rebel team is said to have fired the fatal missile.

It is a massive gamble for the national government. Having locked in the support of much of the West in its battles with Moscow, many of those alliances became even stronger in the wake of what the weight of evidence to date suggests was a rebel missile strike on the Malaysian Airways aircraft on July 17.

But if a military campaign - one that might easily have waited for the few weeks that Canberra and other capitals say are needed to recover the remaining bodies, personal possessions and wreckage of MH17 - makes the crash site inaccessible, those alliances will be sorely tested, particularly given warnings on the site's degradation with each passing day that stalls efforts to set up a full-throttle investigation.

The loss of Donetsk would be a major blow to the pro-Russian rebels. But there’s a risk too that prolonged fighting would rob the foreign investigative effort of Donetsk as a base and at the same time deny it secure passage on the winding, 100 kilometre road from the city to the crash site.

The bright yellow vests worn by the Australian Federal Police, emblazoned with the Australian flag, stood out in a crowd of Australian and Dutch police and forensic experts in the grounds of Donetsk’s Radisson Park Inn for much of Sunday morning – as they attempted to negotiate safe conduct to the crash site with heavily armed rebels – but by lunchtime it had become impossible.

The Australian and Dutch teams, numbering more than 30, were to be guided by conflict monitors from the Organisation for Security and Co-operation in Europe, but on Sunday night the deputy chief of the OSCE mission, Alexander Hug, said safe conduct had been possible for the previous 10 days, but that overnight Saturday, "the situation had deteriorated rapidly".

“Each day we have negotiated access with the rebels. We did it last night but as we saw [this morning] the frontline is not clear – it’s very blurred. And it's very unacceptable for the OSCE to operate in a situation in which we can’t guarantee a certain degree of security for our staff,” he said.

Mr Hug said that on Sunday afternoon he had dispatched a small reconnaissance team in the direction of the crash site, but it had been stopped a little more than halfway to the site. “We were blocked at Shakhtersk, where we saw the impact of mortar and artillery fire.”

The OSCE team must tread a careful diplomatic path. But reading between the lines at a press briefing on Sunday evening, the conflict monitors appeared to be pointing a finger more at Kiev than at the rebels. Mr Hug’s colleague Michael Bociurkiw said the OSCE had developed good communications with the rebels – "and there were no incidents".

He told reporters: “You have seen the security provided for us, they had started to back off and leave the field for us […and] I would go so far as to say [that on Sunday morning] they were concerned about our passage and safety.”

Mr Hug sidestepped a question on the extent to which the stepped-up violence amounted to a contest for control of the crash site. But speaking later to Fairfax Media, he added: “It’s always very difficult to say who is in control because the site is so big … we can’t send a team out when we don’t know who's in charge – [but] the rebels have been in control of the parts of the site we have been going to.”

The Ukrainian military has embarked on a strategy to encircle Donetsk, cutting supply routes to and from the city to small outlying centres, 10 of which it claims to have wrested from the rebels who have declared Donetsk the capital of their so-called Donetsk People’s Republic.

The Australian Federal Police contingent of 11 officers has landed in a ghost town – tens of thousands of residents have fled and those who remain are hunched indoors, in the belief that any day now, Kiev will begin bombarding the city.

Roads and trains leaving the city are reportedly packed and anecdotal evidence suggests that as much as 30 to 40 per cent of the city’s population of 1 million has fled. Shops are boarding up, bomb-shelters are being prepped and there are calls for blood donations. Streets and pavements are deserted and a curfew is in force – from 11pm through to 6am. And the rebels on Sunday accused Kiev of shutting down the local banking system.

There were claims and counterclaims over which side was responsible for 13 deaths in Horlivka on Saturday, including a woman and two children, aged 1 and 5.

Kiev has brushed off the condemnation of the New York-based Human Rights Watch, which warned last week that the national army’s use of unguided rockets in populated areas could amount to a war crime.

Speaking as though Kiev already controlled Horlivka, Ukranian military spokesman Andriy Lysenko said on the weekend that the roadblocks around Donetsk were to deny the rebels reinforcements and supplies of ammunition and equipment.

“The next one will be Donetsk – the city will be liberated,” he said. “The direct route is open for the forces of the anti-terrorist operation to the capital of the Donbass region – the city of Donetsk.”