"I am calling on all sides to carry out the agreed prisoner swap by the end of this year, specifically to exchange the weakest ones," Frank-Walter Steinmeier said in a statement circulated by the German Foreign Office.
A trilateral contact group of envoys from Russia, Ukraine and the Organization for Security and Co-operation in Europe (OSCE) met in the Belarusian capital of Minsk a day before.
Envoys agreed to continue efforts to end fighting between militias and pro-government troops in Ukraine’s southeast in 2017 and confirmed a ceasefire will come into being along the line of conflict at midnight on December 24.
Steinmeier described the indefinite ceasefire as an important signal that comes after a recent flare-up in fighting near the city of Debaltseve in the Donetsk region. He reminded the warring parties they were still to withdraw troops from the contact line and guarantee access to the war zone for OSCE observers.