The Supreme Court of Ukraine has declined a cassation appeal filed by head of RIA Novosti-Ukraine Kiril Vyshinsky on the legality of his detention.

"The unified chamber of the Cassation Criminal Court of the Supreme Court has declined the cassation appeal," Andriy Domansky, a lawyer for Vyshinsky, told Interfax-Ukraine on Monday.

The cassation appeal contested the decision made by the Appellate Court which declined to institute proceedings to contest the legality of the detention.

The lawyer said a full text of the court's decision will be published on June 3 and it is currently not known what its motives were.

Domansky also said Vyshinsky had been kept in a glass box at the Monday court hearing as the court had declined the defense lawyers' motion to allow him to be next to his lawyers at the hearing, which the lawyer believes violates his rights.

Officers of the Ukrainian Security Service detained Vyshinsky in Kyiv on May 15, 2018. They searched the office of the RIA Novosti Ukraine in Kyiv jointly with Kyiv-based "prosecutors of the Autonomous Republic of Crimea." Vyshinsky is suspected of treason.

On May 16, Vyshinsky was taken to Kherson, where the court ordered to take him into custody on May 17. The Kherson City Court has repeatedly extended his arrest, and the court of appeals upheld these rulings.