The foreign ministers of Germany, Russia, Ukraine and France were unable to make enough progress in closed-door meetings Monday on the Ukrainian crisis to move ahead with a higher-level summit.

German Foreign Minister Frank-Walter Steinmeier said their four-hour meeting was a "very open exchange" but did not produce the results needed for the countries to go ahead with a meeting of leaders this week in Kazakhstan.

He said representatives from their ministries would meet instead in the coming days to see if they could bridge differences, and raised the possibility that the foreign ministers could meet again after that.

In a joint statement, the four ministers also called on the contact group of Ukraine, Russia, and the OSCE to meet to try and make progress on implementing a much-violated Ukraine peace deal drawn up in September, including creating the "relevant conditions for an effective cease-fire."