Norway's intelligence service said Monday its agents had arrested a Norwegian man suspected of passing sensitive information to Russia.
"The man is formally suspected of providing information to a foreign country that could damage fundamental national interests," the PST intelligence agency wrote on Twitter.
A PST official later confirmed the country in question was Russia.
"The person arrested held meetings with an officer from the Russian intelligence agency," Line Nyvoll Nygaard told TV2 Nyhetskanalen television.
Meanwhile, DNV GL, a company that provides certification for insurance purposes for the maritime, oil and gas and renewables industries, confirmed the suspect was one of its employees.
"Through his position (he) had access to information which, in our opinion, could be of great interest and significance to other countries and other actors," Nyvoll Nygaard said.
The man, aged 50, was arrested on Saturday in an Oslo restaurant after having met the Russian officer, the PST said.
A judge on Monday ordered the man detained in custody for four weeks, the first two in isolation.
According to his lawyer, he denies any wrongdoing. He risks up to 15 years in prison if found guilty of espionage.
Russia's embassy in Oslo has not commented on the arrest.
In its annual report published in February, PST warned of the risk of espionage in several sectors of society -- political, financial, defense and research circles, among others -- singling out Russia, China and Iran as particular threats.
In recent decades several spy cases have marred ties between NATO member Norway and Russia, which share a border in the Arctic Circle.