The single day death toll of nine was the highest in over a month. Government troops and pro-Moscow rebels have accused each other of gearing up for a renewed fight that would finish off the already shaky February ceasefire agreement.

"We really strongly condemn this escalation of fighting and we call all sides to cease it and to observe the ceasefire," said European Commission spokeswoman Catherine Ray on Monday, speaking to journalists in Brussels.

The Donetsk News Agency, which represents the pro-Russian rebels, said Monday that overnight artillery fire had killed three people in the front line town of Horlivka and two in the rebel capital of Donetsk.

Ukrainian officials, meanwhile, reported two civilian deaths in a suburb of the port city of Mariupol. The Ukrainian Security and Defense Council also reported two troops killed and six injured.

UN Secretary-General Ban Ki-moon said he was "seriously alarmed" by the upsurge in violence, adding that the ongoing "ceasefire violations and the resulting loss of life are unacceptable."

'Preparation for more military action'

Russia, which has been accused by Kyiv and the West of sending troops and weapons across the border to fuel the insurgency, on Monday turned the spotlight on Kyiv, warning that Ukraine could be readying for fresh fighting.

"We are concerned by the course of events in recent days which very strongly resembles the preparation for more military action," said Russian Foreign Minister Sergey Lavrov.

Ukraine's Foreign Ministry criticized the rebels and their alleged backer Moscow for the increase in violence.

"Ukraine calls on Russia to take immediate measures to stop the escalation of the situation," said the ministry in a statement.

In a move that further angered Kyiv, Russian President Vladimir Putin visited Crimea Monday to discuss the region's faltering development under Moscow's rule. Ukrainian President Petro Poroshenko described Putin's visit as a "challenge to the civilized world."

The United Nations says the conflict has cost more than 6,800 lives since April 2014 and has driven at least 1.4 million people from their homes.

av/cmk (AP, AFP)