Security services in Norway have charged a university lecturer with gathering illegal intelligence and claim to have uncovered his real identity.
The suspect, said to be in his 30s, had posed as a Brazilian academic, but officials claim he is a Russian spy.
He has been named in Norwegian media as Russian national Mikhail Valerievich Mikushin.
The suspect's lawyer has said he denied the charges.
Earlier in the week, Norwegian officials said the man had a Brazilian passport and had worked as a researcher at the University of Tromsoe in the north of the country since 2021.
Now more details have been released.
In comments quoted by Norwegian media on Friday, security services spokesman Thomas Blom said the suspect had been charged with gathering intelligence linked to state secrets.
Blom also stated that they believed the man - who has reportedly been going by the name José Assis Giammaria - was not who he claimed to be.
The suspect is also believed to have lied about his age, and is in fact 44 rather than 37 years old, Blom said.
Christo Grozev of the Netherlands-based investigative journalism group Bellingcat believes the man is a colonel linked to Russian military intelligence, the GRU.
In a tweet, Grozev claims to have found information which links the accused man's supposed Russian name to a GRU boarding school.
So we now know there's no Jose and the guy is a Russian spy called Mikhail Mikushin, 6 years older than his adopted identity (man, he wanted to be younger). But how do we know which intelligence service he is from? Let's check his address history in Russia.
— Christo Grozev (@christogrozev) October 28, 2022
"Good job, Norway - you have secured a colonel from the GRU," Grozev wrote.
Asked by Norwegian news site NRK about the suspect's potential links to the GRU, his lawyer said she did not want to comment on the information from Bellingcat.
The Russian embassy in Oslo reiterated to Norwegian media that it did not know who the man charged with espionage was and had no further comment on the new information.
In recent weeks, Norway's security services have arrested several Russian citizens accused of working for Russia as spies. Eight people have been arrested for flying drones near, or taking pictures of, critical infrastructure.
The country - a key Nato member that has replaced Russia as the biggest gas supplier to Europe - has been concerned by sightings of drones near critical oil and gas infrastructure.
-BBC