Ukrainian President Petro Poroshenko has said he is ready to consider allowing humanitarian assistance into the rebel-held area of eastern Ukraine.
But he said any such mission must be international and unarmed and only enter via Ukrainian-manned checkpoints.
Russia has repeatedly called for a humanitarian mission but the West fears it could use it to send in troops.
Meanwhile, pro-Russian separatists have called for a ceasefire in Donetsk to avert a "humanitarian catastrophe".
Rebels said the Ukrainian army had taken the key town of Krasnyi Luch and encircled Donetsk.
Reports from the city of Luhansk, second only to Donetsk in its importance to the rebels, also suggested living conditions were dire.
More, plus video report: http://www.bbc.co.uk/news/world-europe-28730223