The German government on Monday voiced concerns over the lack of a comprehensive ceasefire in Ukraine which should have taken effect more than a week ago.

Germany is not satisfied with the course of implementation of the agreements reached in Minsk, German government spokesman Steffen Seibert said.

"What is decisive is a comprehensive cease fire. It is worrying for the German government that we haven't seen anything like this yet," he said.

The peace initiative of the leaders of Germany, France, Russia and Ukraine unveiled in Belarus’ capital Minsk earlier this month provided for a ceasefire from the start of 15 January, withdrawal of heavy weapons by the Ukrainian government forces and pro-Russian rebels as well as measures on long-term political settlement in Ukraine, including enforcement of the special self-rule status for certain areas of the Donetsk and Luhansk regions.

"When you look at the situation as a whole since leaders met in Minsk, it is clear the implementation of the agreed measures is not satisfactory," Seibert said.

Ukraine said earlier on Monday that it won't withdraw its heavy weapons as provided for by the Minsk agreement because the pro-Russian separatists kept violating the ceasefire agreement.

"As long as the rebels keep firing at Ukrainian soldiers' positions, we cannot talk about pulling back heavy weapons," Ukrainian media quoted Defence Ministry spokesman Vladislav Seleznyov as saying in Kiev. According to Seleznyov, a ceasefire must hold for at least 24 hours before a withdrawal can start.

The separatists refuted the allegations with rebel leader Eduard Basurin saying that government forces had violated the ceasefire 29 times in the 24 hours to Monday morning by firing upon separatist positions in southeastern Ukraine.