Fighting erupted overnight between Ukrainian government forces and Russian-backed separatists in the east of the country, leaving several civilians dead.
Regional police said at least two people were killed when rebels shelled the town of Sartan. While a separatist website said three had been killed by government shelling in Gorlivka.
The clashes near Mariupol mark an increase in violence which has further strained the delicate ceasefire.
It comes as both sides are accusing the other of preparing to launch an offensive.