The February 2015 Minsk cease-fire deal failed to completely halt the conflict that is now in its third year.
Both sides accuse the other of violating the terms of the truce — which includes a pullback of heavy weapons — and casualties among soldiers or civilians are reported almost daily.
"We have been registering with great concern the deterioration of the situation in the east for months now," said Ertugrul Apakan, chief monitor of the Organization for Security and Cooperation in Europe's monitoring mission to Ukraine.
"It is regrettable that the sides did not heed our many calls for restraint," he said in an emailed statement.
The continued fighting has helped sap public confidence in Ukraine's Western-backed leadership, which underwent its biggest reshuffle since December 2014 this week with the appointment of a new prime minister and cabinet.
Twenty Ukrainian soldiers were reported killed in March — the army's highest monthly death toll since August, while seven have been killed so far in April, according to Reuters calculations based on military data.
In the past 24 hours, Ukrainian positions on the front line experienced the heaviest attack from mortar and light weapons since Aug. 27, military spokesman Colonel Andriy Lysenko said in daily televised briefing.
The government-held town of Avdiyivka, north of rebel-controlled Donetsk, was the focus of the majority of the attacks, he said.
Over 9,300 people have been killed since fighting between Ukrainian troops and rebels seeking independence from Kiev erupted in April 2014.
Kiev accuses Russia of seeking to destabilize Ukraine for seeking closer ties with Europe by supporting the separatists with weapons and fighters — a charge the Kremlin denies.
Source: Voice of America