Chancellor Angela Merkel Tuesday told Russian President Vladimir Putin to use his influence to rein in pro-Kremlin rebels in eastern Ukraine, a day after the German leader warned that a peace deal was not being fully implemented.

During a phonecall, Merkel "made it clear to President Putin that in order to obtain further progress towards a comprehensive political solution", a ceasefire had to be respected and unfettered access given to observers monitoring the truce.

"Here, Russia must use its influence on the separatists," she said, according to a statement issued by her spokesman.