Speaking after a round of talks with the Ukrainian president's chief of staff Andriy Yermak in Minsk, Belarus, Kozak said that they also discussed ways of political settlement of the conflict in eastern Ukraine.
The conflict in Ukraine's eastern industrial heartland flared up in April 2014 weeks after Russia annexed Ukraine's Crimean Peninsula. The fighting has killed more than 14,000.
In December, leaders of Ukraine, Russia, France and Germany made a deal to exchange prisoners and take new steps to ensure a lasting cease-fire in fighting between Ukrainian troops and Russia-backed separatists. They made no immediate progress, however, on key contentious issues — a timeline for local elections in eastern Ukraine and when Ukraine can get back control of its borders in the rebel-held region.