A Russian court has extended the detention of a Norwegian man suspected of spying after he allegedly received classified documents from a Russian man who is also under arrest.

The Lefortovo District Court in Moscow on February 2 ordered that Frode Berg should remain in jail until May 5.

Berg, 62, was allegedly caught receiving classified material about the Russian Navy that he is accused of planning to hand over to Norwegian and U.S. intelligence agencies.

He has denied the charges.

"We still do not know if Berg fell into a trap, or if, without knowing it, actually became involved in a real intelligence operation," Ilya Novikov, Berg’s lawyer in Moscow, was quoted by the Norwegian newspaper Aftenposten as saying.

Norwegian media have reported that Berg is a former border inspector and that the Norwegian Foreign Ministry has been working to provide him with assistance.

Some reports have 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 Dagens Naeringsliv, AP, and TASS