MOSCOW (Reuters) – State prosecutors have charged a prominent Russian scientist with treason after accusing him of passing state secrets to China, his lawyer said on Monday, saying his client could serve up to 20 years in prison if found guilty.

Valery Mitko, president of the Arctic Academy of Sciences in St. Petersburg, has been under house arrest since authorities charged him with high treason in February.

Ivan Pavlov, his lawyer, said the 78-year-old academic travelled to China twice a year to speak as a guest lecturer and denied handing state secrets to the Chinese authorities.

Mitko did travel to China with documents for his lectures, but these contained academic and open source information only, Pavlov said.

“There were no state secrets in there at all. We consider these accusations to be absurd,” Pavlov said, saying he hoped the case would be dismissed before trial.

A source told the Interfax news agency that Mitko has been accused of having given China information pertaining to methods used to detect submarines.

A number of Russian scientists have been arrested and charged with treason in recent years for allegedly handing sensitive material to foreigners. Critics of the Kremlin have said these arrests stemmed from unfounded paranoia.