Ukraine says that three of its servicemen have been killed and nine wounded in the previous 24 hours in the country's east.
The casualties underscore the fragility of a two-week-old cease-fire between government forces and Russian-backed separatists in a conflict that has killed more than 6,000 people since April.
A military spokesman said on March 3 that rebels shelled Ukrainian positions 22 times over the past day.
Meanwhile, separatists accused Ukrainian troops of firing mortar shells in the outskirts of Donetsk overnight.
On March 2, Kyiv said the leaders of Ukraine, Russia, France, and Germany agreed to send OSCE observers to areas of Ukraine where violations of the truce have been reported.
A German government spokesman said the leaders agreed that the OSCE should play a greater role as observers of the Minsk cease-fire agreement.