Russia has artificially delayed the replacement of the Ukrainian border group at their "Donetsk" checkpoint, Ukrainian Border Service head Petro Tsyhykal has said.

"The Russians periodically contact heads of border patrol squads at border control points at various levels… This happened yesterday. They are trying to find reasons to initiate a working dialogue and pretending nothing is happening, trying to accomplish technical tasks," Tsyhykal said in an exclusive interview with the Kyiv-based Interfax-Ukraine news agency.

As for the Anti-Terrorist Operation zone and administrative borders with temporarily occupied Crimea, he said all contacts from the occupier's side come to naught.

"Issues arose connected with the arrival of our group to their "Donetsk" checkpoint. Our border troops are there and fiscal service agents conduct visual reconnaissance of Russia's so-called humanitarian convoys. The Russian side not long ago deliberately delayed giving approval to replace our detachment there," Tsyhykal said.

The head of Ukraine's Border Service said the maximum length of time the detachment could be on Russian territory is 90 days.

"The Russian side delayed rotation as long as possible in order to have grounds to accuse the group of violating migration legislation. As a result, after involving international organizations, including the Organization for Security and Cooperation in Europe, we were able to rotate them out," he said.