On Friday the US State Department expressed concern at what appeared to be a crumbling ceasefire in Ukraine, and events in Donetsk appear to show an escalation of fighting for the airport, which pro-Russian separatists claim they have recaptured from government forces.

There are also reports of a heavy buildup of Russian forces on the Russian side of the frontier.

The separatists continue to control many key points in the city, and the Ukrainians continue to accuse them of deliberately firing from residential buildings to prevent a riposte, or gain propaganda from a reply that produces civilian casualties.

The Red Cross has been active in the city for months but on Thursday it suffered its first fatality in the Ukrainian conflict when a Swiss aid worker was killed by an artillery shell that hit close to the ICRC office. Both sides blame the other for firing it.