Norway’s domestic security agency has arrested a university lecturer suspected of being a Russian spy.

The man entered the country as a Brazilian citizen and had been detained, said Martin Bernsen, a spokesman for the Norwegian Police Security Service, known as PST.

He said the case was “huge”.

The man was detained on Monday in the Arctic city of Tromso, the public broadcaster NRK said, adding that investigators believe he was in Norway under a false name and identity while working for one of Russia’s intelligence services.

The PST deputy chief Hedvig Moe told NRK that the man had been based at the Arctic University of Norway in Tromso as “a Brazilian researcher” and would be expelled from the country “because we believe he represents a threat to fundamental national interests”.

The security service “is concerned that he may have acquired a network and information about Norway’s policy in the northern region,” Mr Moe said. “Even if this network or the information bit by bit is not a threat to the security of the kingdom, we are worried that the information could be misused by Russia.”

Mr Moe told NRK the Norwegian agency had collaborated with the security services of other unspecified countries.

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“International co-operation is important in the work with illegals because they are very careful and are often good at hiding and operating for a long time in the country,” he said.

Jørgen Fossland, the university’s administrator, said the person in question was “a guest lecturer” and was apprehended on his way to work on Monday.

The man, who has neither Russian nor Norwegian citizenship, arrived in the country last year and has researched the northern regions and hybrid threats, Norwegian media wrote. Norway’s Arctic border with Russia is 123 miles long.

The man’s lawyer, Thomas Hansen, told the VG newspaper he denies any wrongdoing. On Tuesday the man was detained for four weeks by a local court.

Several Russian citizens have been arrested in Norway in recent weeks.

Three men and a woman were allegedly seen taking photos in central Norway of banned objects. They have since been released.

European nations have increased security around key energy, internet and power infrastructure after underwater explosions ruptured two natural gas pipelines in the Baltic Sea that were built to deliver Russian gas to Germany.