Ukraine's military has said pro-Russian rebels were amassing heavy weapons in depots around the separatist-held city of Donetsk, despite a ceasefire deal.
Attacks have fallen in the past week, but accusations from both sides of violations show the fragility of the peace deal agreed in Minsk last month, which calls for the withdrawal of heavy weapons from the frontline.
"(Rebels) are continuing to transport equipment and artillery ammunition intensively via the Debaltseve railway junction and build weapons storages around Donetsk," military spokesman Andriy Lysenko said in a televised briefing.
The Organization for Security and Cooperation in Europe,which monitors the pull-back of weapons, has said it cannot fully confirm withdrawal on both sides as it has not been given access to all the locations where some weapons have been moved.
Mr Lysenko said Ukrainian positions had come under attack from separatists 31 times on Monday, including five instances of artillery fire, and reported nine servicemen had been wounded in the past 24 hours.
"The most troubled areas are Shyrokyne and around Donetsk airport ... yesterday there was fighting almost all day in Shyrokyne," Mr Lysenko said, referring to a village on the outskirts of government-held Mariupol, a strategic port city the Ukrainian government fears could be the focus of the next rebel offensive.
On the rebel side, officials said Ukrainian forces had violated the ceasefire 17 times in the past 24 hours, butr eported no casualties, separatist press service DAN said.
Earlier Ukrainian President Petro Poroshenko said separatists had withdrawn a significant amount of weaponry from the front-lines in eastern Ukraine in accordance with a three-week-old ceasefire deal.
"Ukraine has withdrawn the lion's share of its rocket and heavy artillery systems. The Russian-backed fighters have also withdrawn a significant amount," Mr Poroshenko said in a televised interview.
While the Minsk agreements have been broadly observed along the front lines in the past two weeks, Kiev has accused the rebels of continuing to fire on government positions and using the truce to regroup their forces and rearm for a further offensive, a charge the rebels deny.
Mr Poroshenko said 64 Ukrainian servicemen had been killed since the ceasefire was meant to come into force on 15 February.
Nearly 6,000 people have been killed since the conflict between government troops and separatists erupted last April.
Meanwhile, the Russian defence ministry said it had launched military exercises in the country's southern region of Stavropol, the news agency RIA Novosti reported.
The exercises involve artillerymen and multiple launch rocket systems, the agency reported, citing a statement.
