Ukraine’s security council is expected to hold an emergency meeting on Sunday, in the wake of deadly rocket attacks in the eastern city of Mariupol.
Local officials say at least 30 people were killed and more than 80 injured in Saturday’s violence.
Rocket fire reportedly slammed into a market, schools, homes and shops.
It came after rebels announced they were going on an offensive against the Kiev government to take more territory.
US Secretary of State John Kerry has joined his EU counterparts in condemning the attacks. He is calling on Russia to end its support for the rebels.
Moscow denies sending forces and weapons to eastern Ukraine.