The Ukrainian military says two of its servicemen have been killed and three wounded in fresh separatist attacks in the east.
Military spokesman Andriy Lysenko told a news conference, "Around Donetsk, particularly near the airport, there is military action practically round-the-clock ... The enemy has pulled banned weapons into Donetsk -- tanks and high-caliber guns -- and is actively using them."
The situation near the strategic Kyiv-controlled port city of Mariupol in southeast Ukraine was also "extremely tense" on June 21, with rebels using artillery and sniper fire to attack government positions, Lysenko said.
Meanwhile, separatist officials said there had been no significant attacks on rebel-held territory by Ukrainian forces over the weekend.
Both sides accuse the other of regularly violating a cease-fire deal signed in Minsk in February, but a surge in fighting in the past few weeks has caused international monitors to warn of a threat of a wider escalation.
Based on reporting by Reuters and Interfax