The Kremlin has accused Kyiv of obstructing their officers' work in Donbass and cutting them off from the front line.
Ukraine's security service have detained a government official who allegedly worked "in the interests of the enemy state."
The two leaders agreed on a deal to bring Russian ceasefire observers back to eastern Ukraine.
Local media reported the man as the prime minister's assistant, who accompanied him on key trips.
All Sources: Deutsche Welle Deutsche Welle