A verdict in the trial of 63-year-old Frode Berg is expected on April 16, prosecutor Milana Digayeva was quoted by the Interfax news agency as saying.

She urged that Berg serve the sentence in a strict penal camp, Interfax said.

Berg's trial was held behind closed doors and he rejects the charges brought against him.

The Norwegian was detained in Moscow in 2017 following a sting operation by Russia's FSB security service.

A former Russian police officer accused of handing Berg files on the Russian navy was sentenced in December to 13 years in prison.

Berg admitted to acting several times as a courier for the Norwegian intelligence services, but said he thought he was only carrying money.

President Vladimir Putin commented on the case Tuesday during a meeting with Norwegian Prime Minister Erna Solberg after hosting the International Arctic Forum in Saint Petersburg.

"As in any country, our courts determine the punishment, responsibility and guilt or innocence" of a person accused of committing a crime, Russian agencies quoted Putin as saying.

Asked if Berg could possibly be pardoned, Putin remarked that "a person can only be pardoned if he has been convicted. He has not been convicted yet."

Norway, a NATO member, normally enjoys good relations with neighbouring Russia, with which it shares a short land border.

But those relations have grown more tense since 2014, when Russia annexed Crimea and a pro-Russian insurgency erupted in eastern Ukraine.