Heavy shelling has been heard in the rebel-held Ukrainian city of Donetsk as a Russian convoy approaches the Ukrainian border.
Initial reports say people poured out of offices in the centre of the city after an evacuation warning sounded.
Donetsk has been surrounded for several weeks by Ukrainian forces battling pro-Russian rebels.
Meanwhile, more than 100 lorries carrying Russian aid are approaching a rebel-controlled border crossing.
There is continuing confusion over their final destination. On Thursday afternoon, the lorries had got to within a few miles of the border, where they had parked in a field, reports the BBC's Steve Rosenberg, who is following the convoy.
Russia has dismissed as absurd claims that its convoy is a pretext to send military supplies to the rebels.
But Ukraine has said the Russian convoy must be inspected by international monitors before it can be let in.
The situation is reported to be desperate in the rebel-held city of Luhansk, where civilians have been short of water, food and electricity for more than a week. Phone lines are also down as shelling continues.
A senior International Red Cross (ICRC) official, Laurent Corbaz, is flying to the Ukrainian capital Kiev and then on to Moscow to discuss the Russian aid initiative.
The ICRC says Ukraine and Russia need to clarify border crossing procedures.