German Chancellor Angela Merkel stressed on Wednesday Moscow's "responsibility" to act as a moderating influence over the pro-Russian separatists in Ukraine.

"The ceasefire in place in eastern Ukraine "must be strictly respected", a statement by a German government spokesman cited Merkel as saying during a telephone call with Russian President Vladimir Putin.

"The two leaders shared the same concerns over the persistent violence in Ukraine," the statement added.

She "insisted on Russia's responsibility to exercise a moderating influence on the pro-Russian separatists," it read.

The Ukraine-Russia border should be properly monitored, the statement continued, stressing the importance of the role played by the Organization for Security and Cooperation in Europe (OSCE), charged with overseeing the ceasefire signed a month ago.

Clashes have raged for days at several flashpoints around the region, with the Ukraine authorities and the pro-Moscow rebels blaming each other for violating the agreement that commits them to withdrawing weapons and establishing a buffer zone.