A Russian scientist has been detained in Siberia for allegedly passing technology to China, Russian media reported on Thursday. Alexander Lukanin, a 64-year-old scientist from the Siberian city of Tomsk, was detained on Tuesday after returning from China were he had been working at a local university, according to MBKh Media, a news outlet founded by Kremlin critic Mikhail Khodorkovsky.

Lukanin’s apartment was also raided by the FSB security service, MBKh Media reported, citing one of the scientist’s friends. A message sent by Reuters on Thursday to Lukanin’s email address went unanswered. There was no immediate comment from the Russian or Chinese authorities.

Under Russian law, illegally transferring technology to a foreign country can lead to up to three years in prison. Interfax news agency quoted a source as saying Lukanin had been detained for allegedly passing technology to China but that he was not being accused of passing state secrets, something that could carry a heavier prison term.

A number of Russian scientists have been arrested and charged with crimes such as treason in recent years for allegedly handing sensitive material to foreigners, including Chinese nationals. Kremlin critics say the arrests often stem from unfounded paranoia.

In February, Valery Mitko, a scientist heading the Arctic Academy of Sciences in St. Petersburg, was charged with treason after he was accused of passing state secrets to China. Like Lukanin, Mitko had travelled to China to work at a university.

Despite the misgivings of some nationalist politicians, Russia has increasingly prioritised closer ties with China, especially since its relations with the West collapsed because of its annexation of Crimea from Ukraine in 2014.