SBU head's adviser Yurii Tandit told Censor.NET.
Answering a question of whether Ruban was detained, he said: "He is being questioned."
Tandit said to inquire the State Border Guard Service for details.
Later, SBU spokesperson Olena Hitlianska said:
"SBU is questioning!!! Volodymyr Ruban in the Donetsk region in connection with his violation of the demarcation line crossing in the ATO [anti-terrorist operation - ed.] area. Possible cancellation of citizen V. V. Ruban's permit for crossing the contact line is also being considered. The law is for everyone!"
Earlier, Ruban's detention was announced by Hromadske Radio journalist Iryna Sampan.
"Head of Ofitserskyi Korpus Ukrainian Center for Prisoners Release Volodymyr Ruban was detained by the Security Service of Ukraine (SBU) at Marinka checkpoint. He was traveling to the unrecognized "DPR" to pick up Nadiia Savchenko. The secret services have been working with him for several hours now," Sampan wrote.