France's President Francois Hollande on Thursday denounced as "unacceptable" ceasefire violations in eastern Ukraine, after speaking briefly with his Ukrainian counterpart Petro Poroshenko in Germany.

"There are ceasefire violations today and that's unacceptable," Hollande told reporters, adding that "there is a risk of fresh unrest and we need to warn them of that."

Some of these "groups have an interest in making this conflict last and we know which groups these are easily," he said, without giving further details when asked about the violations.

At the same time, Hollande said he also reminded Poroshenko that Kiev also needs to "respect a certain number of conditions."

The French president added that during his impromptu conversation lasting 15 minutes with Poroshenko, the two leaders discussed the implementation of the Minsk truce accord.

He also stressed that France wanted to see the Minsk deal implemented in full.