Donetsk on a hair trigger as investigators stalled

Shellfire pounds into border towns, watched by panicking locals as a column of Ukraine armoured vehicles heads towards the battle zone.

It's been some of the worst fighting in Ukraine's war with Russian-backed separatists.

It has also stalled the Australian-led effort to find the still missing victims, and the truth behind the downing of MH-17.  

The fact that the crash site is in a war zone poses a logistical nightmare and yesterday teams of Australian and Dutch investigators had to abandon attempts to get there. 

They hit the road in a convoy led by European monitors who have been negotiating with government forces and separatists to gain them safe passage.

It is never easy - all last week, we were able to make the two-hour drive every day from the regional capital of Donetsk to the crash site.
 
But on our last attempt, earlier today, we witnessed new urgency and military strength along this road.
 
More army vehicles, and more Ukraine troops manning road-side strong-points and weapon pits.
 
Some of these positions, just a few days ago, were in rebel hands. Today federal troops, in a new offensive, are in command.
 
Meanwhile, more of our federal police have arrived in the Ukraine capital Kiev.

Before they can begin their work there will need to be a long-term pledge of cooperation from the rebels.

That might be wishful thinking. This whole region remains on a hair-trigger.