The Security Service of Ukraine (SBU) is questioning the leader of the prisoner-release center the Officers' Corps, Volodymyr Ruban, and will soon question Rada deputy Nadia Savchenko as well.

"We are now questioning [Ruban] over the instance of his violation of the established rules for crossing the dividing line in the ATO [anti-terrorist operation] zone," SBU spokeswoman Olena Hitlianska told Interfax-Ukraine on Monday.

The questioning is taking place in Donetsk region. Ruban is not under arrest, she said.

The contact line crossing procedure is set out in Article 415 of the Anti-Terrorist Center provisions and is freely available, Hitlianska said.

"Furthermore, we are considering canceling permission for Volodymyr Ruban to cross the contact line," the SBU spokeswoman said.

Asked whether the SBU is going to question Savchenko, as was reported earlier, Hitlianska said: "Savchenko too will be invited for questioning, including on this matter [over violation of the rules for crossing the contact line]."

On February 24 Savchenko and Ruban arrived in Donetsk and later visited a jail in Makiyivka where Ukrainians are held prisoner.

Meanwhile, the SBU announced its intention to speak to Savchenko on the subject of her visit to Ukrainian prisoners-of-war in Donetsk and check Rada lawmaker Tetiana Rychkova's allegations that Savchenko "incited active Ukrainian military servicemen to topple the government."