Russia is holding a Norwegian man on suspicion of spying after he allegedly received classified documents from a Russian man who is also under arrest, an official said on December 19.

Frode Berg was ordered held in custody by Moscow's Lefortovo District Court on December 6, the Interfax news agency quoted court spokeswoman Yekaterina Krasnova as saying.

Berg has appealed the decision but a date for the hearing on his appeal has not yet been set, Krasnova said.

Russian media reports cited unnamed sources as saying that Berg was caught receiving classified material about the Russian Navy that he allegedly planned to hand over to Norwegian and U.S. intelligence agencies.

According to Interfax, Russian authorities allege that Berg was given the classified material by Aleksei Zhitnyuk, a Russian man who was arrested in late November on suspicion of treason.

Norwegian media reports said that Berg, 62, is a former border inspector and that the Norwegian Foreign Ministry was working to provide him with assistance.

Some reports suggested his arrest could be linked to what they said was his opposition to the construction of a fence along a small part of Norway's short border with Russia.

Norway built the 200-meter fence in 2016 after thousands of asylum seekers, many of them from Syria, crossed from Russia into Norway at the border post.

The reports come eight days after a Moscow court convicted an Estonian businessman of espionage and sentenced him to 12 years in prison.

Russia has imprisoned several people from neighboring countries including Estonia, Lithuania, and Ukraine on espionage charges, with tension rising over Moscow's seizure of Crimea in 2014 and involvement in a war against Kyiv's forces in eastern Ukraine.

Kremlin critics say Russia uses spy claims as a tool in geopolitcal competition.

Russian courts usually hold espionage trials behind closed doors, citing what they say is the need to protect classified information and state secrets.

With reporting by Interfax, Rosbalt, RIA, NRK, BBC, and vg.no