A Moscow court has sentenced a 63-year-old Norwegian, Frode Berg, to 14 years in a strict-regime labour camp for spying on Russian navy submarines.
Berg, arrested in Moscow in 2017, denied the accusation.
He formerly worked as a guard on the Norwegian-Russian border.
Berg admitted acting as a courier for Norwegian intelligence, but said he had little knowledge of the mission. A Russian ex-policeman accused of passing him navy files has been jailed.
Berg's lawyer, Ilya Novikov, said his client would not appeal against the verdict but would seek a pardon from President Vladimir Putin.
Norway - a Nato member - shares an Arctic border with Russia and for decades their relations were amicable, even during the Cold War. But ties have worsened since 2014, when Russia annexed Ukraine's Crimea peninsula.
Mr Novikov, quoted by AFP news agency, said Berg "expects his government to undertake diplomatic efforts" and "we see no practical use in appealing".
"He's been used without his knowledge," Mr Novikov said. "We cannot talk about gathering any secret information."
He warned that, at the age of 63, Berg was facing "basically a life sentence".