A separatist leader proposed a ceasefire after troops loyal to Ukraine's government surrounded Donetsk, home to about 1 million people before the conflict began in April, but a city that has since seen hundreds of thousands of people flee. Ukraine's four-month conflict has claimed more than 1,300 lives and the United Nations has warned of a deteriorating human rights situation.

"We are ready for a ceasefire to prevent the proliferation of a humanitarian disaster in the Donbas," Aleksandr Zakharchenko, the prime minister of the self-proclaimed Donetsk people's republic said of the broader Donbas region containing Donetsk. Zakharchenko took over the position in Donetsk on Thursday evening after the surprise resignation of his predecessor Alexander Borodai.

A Donetsk official said army shelling killed one person Saturday and injured 18. On Friday, Ukraine's military announced it had reclaimed two villages. Thirteen security personnel were killed within 24 hours, the army reported.

'We are ready'

President Petro Poroshenko told German Chancellor Angela Merkel on Saturday that Ukraine would accept an international aid mission in the east, but only an unarmed team entering through government-controlled borders.

Poroshenko said the two discussed the potential for Germany's participation.

"We are ready to accept humanitarian aid if the mission is an international one, without any military escort and if it passes through border checkpoints controlled by Ukrainian guards," Poroshenko said.

On Friday, Ukraine claimed to have turned back a Russian military convoy posing as an aid mission - a report Russia dismissed as a "fairy tale."

Merkel also spoke with US President Barack Obama on Saturday. According to the White House, they said that any Russian intervention in Ukraine without Kyiv's approval would not be tolerated.

"The two leaders agreed that any Russian intervention in Ukraine, even under purported 'humanitarian' auspices, without the formal, express consent and authorization of the government of Ukraine is unacceptable, violates international law, and will provoke additional consequences," the White House said in a statement.

mkg/msh (Reuters, AFP, dpa, AP)