The Ukrainian military says one serviceman has been killed and 10 have been wounded as a result of fighting in the country's eastern territories in the past 24 hours.
Military spokesman Andriy Lysenko said in a briefing on June 6 that areas northwest of separatist-controlled Donetsk were among the worst hit by pro-Russian rebels' artillery fire overnight.
Both sides accuse the other of using heavy weapons banned under a four-month-old cease-fire deal.
The separatists said Ukrainian forces had bombarded Donetsk overnight with artillery.
"The sound of heavy weapon fire could be heard in practically all districts," separatist press agency DAN reported the rebel-controlled city administration as saying.
On June 5, a senior monitor for the Organization for Security and Cooperation in Europe (OSCE) said the security situation in eastern Ukraine had deteriorated in recent days and accused both sides of putting civilians at risk by positioning military forces alongside civilian areas.