The director of a top Russian science institute, arrested on suspicion of treason along with two other hypersonic missile technology experts, stands accused of betraying secrets to China, two people familiar with the case said.

Alexander Shiplyuk, head of Siberia's Khristianovich Institute of Theoretical and Applied Mechanics (ITAM), is suspected of handing over classified material at a scientific conference in China in 2017, the sources said.

The 56-year-old maintains his innocence and insists the information in question wasn't classified and was freely available online, according to the people, who will not be identified in this report in order to safeguard their security.