At least 30 people were killed in rocket attacks in the city of Mariupol in the east of Ukraine, as pro-Russian rebels announced a major offensive.
The rockets are thought to have come from rebel-held areas, but Alexander Zakharchenko, head of the self-proclaimed Donetsk People's Republic, said his forces had not carried out "active operations" against the city until Saturday.
The attacks were widely condemned, including by the EU who warned “would inevitably lead to a further grave deterioration of relations between the EU and Russia”, according to EU foreign affairs chief Federica Mogherini.
Ertuğrul Apakan, chief of the Organisation for Security and Co-operation in Europe mission, called for an immediate ceasefire. “Ukraine and its people need and deserve peace. The parties must return to the negotiating table without further delay,” he said.
The UN human rights office said the conflict in Ukraine has left 5,000 people dead, including 262 in the past nine days.