Ukraine's military said on Monday one Ukrainian serviceman was killed and four wounded in separatist eastern territories in the past 24 hours, underscoring the fragility of a two-week-old cease-fire deal.
Nonetheless, Ukraine reported a sharp drop in attacks from pro-Russian separatists over the weekend and said it was continuing to pull back heavy weapons from the front line.
But it warned that rebels were using the truce to regroup for new attacks on government positions.
Military spokesman Andriy Lysenko also said pro-Russian rebels continued to receive a "significant" amount of military equipment from neighboring Russia. Moscow has repeatedly denied that it is arming the separatists.
"The enemy is moving heavy weapons and military equipment, primarily in the area of Mariupol," Lysenko said in a televised briefing, referring to a government-held port city that Kiev fears could be the next rebel target.
A fall in the number of attacks and moves by both sides to withdraw heavy weapons from the front line had raised hopes that a fragile truce could hold, even after rebels disavowed last month's peace deal to seize the transport hub of Debaltseve.
"If the situation doesn't worsen, then the Ukrainian side will continue to pull back weapons. For now the process of withdrawal is ongoing," Lysenko said.
Senior rebel commander Eduard Basurin said Sunday that separatists had completed their withdrawal of weapons and denied accusations from Kiev the arms were being returned to the front line, rebel press service DAN reported.
The deputy head of the Organization for Security and Cooperation in Europe's mission in Ukraine has said the OSCE needed details on where withdrawn weapons were being stored, before it could confirm a real pull-back was taking place.
