Police in Norway have opened a corruption investigation into the country's former Prime Minister Thorbjørn Jagland over his alleged links to the late convicted sex offender Jeffrey Epstein.

A special Norwegian police unit which is analysing newly released Epstein files in the US said the 75-year-old was suspected of "aggravated corruption".

Police said they had already asked the country's foreign ministry to lift his immunity, which he enjoys because of his past role as a senior foreign diplomat.

Jagland is also a former head of the Norwegian Nobel Committee and spent 10 years as secretary general of the Council of Europe.

His lawyer said they would fully co-operate with the investigation.

Pål K. Lønseth, head of Økokrim - the economic crime unit investigating Jagland - said: "We consider there are reasonable grounds for investigation, given that he held the positions of chair of the Nobel Committee and Secretary General of the Council of Europe during the period covered by the released documents.

"Among other things, Økokrim will investigate whether gifts, travel and loans were received in connection with his position."

The police added that further details would be given "at a later stage".

Norwegian Foreign Minister Espen Barth Eide said it was "important that the facts of this case are brought to light".

He added that Oslo would ask the Council of Europe for Jagland's immunity to be revoked.

Jagland's lawyer Anders Brosveet welcomed the opening of the investigation.

"Based on what we have found so far, we are confident of the outcome," he told Reuters news agency.

Separately, Brosveet told Norway's VG news site that he and his client would submit "the key findings and documentation we have to Økokrim as soon as practically possible".

Jagland was Norway's prime minister in 1996-97, and the secretary general of the Council of Europe in 2009-19.

He also chaired the Norwegian Nobel Committee in 2009-15.