A Dutch WikiLeaks associate who went missing under mysterious circumstances a year ago probably had a kayaking accident, Norwegian police said, adding that his body has not yet been found.

Key points: Arjen Kamphuis has not been seen since he left his hotel in the northern Norwegian town of Bodo on August 20, 2018

Arjen Kamphuis has not been seen since he left his hotel in the northern Norwegian town of Bodo on August 20, 2018 Then police discovered a kayak in the same area where some of Kamphuis's personal belongings had been found

Then police discovered a kayak in the same area where some of Kamphuis's personal belongings had been found Mr Kamphuis' body has not been recovered, according to police

Arjen Kamphuis, a cybersecurity expert who was 47 years old at the time, had not been seen since he left his hotel in the northern Norwegian town of Bodo on August 20, 2018.

His disappearance had triggered a wave of conspiracy theories on social media, ranging from CIA and Russian involvement to a mission to carry out a secret project for WikiLeaks founder Julian Assange.

Then police discovered a kayak in the same area where a fisherman had found some of Kamphuis's personal belongings floating in the waters about 50 kilometres east of Bodo.

"The police have concluded that Mr Kamphuis most likely suffered an accident in the evening of August 20, 2018, while kayaking in the Skjerstad Fjord a few kilometres north of the village of Rognan in Nordland County in northern Norway, and was subsequently lost at sea," the police said in a statement.

"His body has still not been recovered," they added.

WikiLeaks, which published secret US military documents and diplomatic cables in 2010, called Kamphuis's disappearance "strange".

The mystery deepened when a phone linked to Kamphuis was briefly switched on in an area near the south-western city of Stavanger, located 1,600 kilometres from Bodo, on August 30 last year.

But on Friday (local time), police explained that two truck drivers from eastern Europe had found the phone, a laptop and other items belonging to Kamphuis while they were fishing in the spot where his kayak was found and took the items with them.

"The police have no reason to believe that the truck drivers were involved in the disappearance of Mr Kamphuis in any other way," the police statement said.

Assange to remain in jail

The update from Norwegian police came as a judge ruled Julian Assange must remain in prison when his jail term ends, because he is at risk of absconding.

Assange will be eligible for release from a prison in south-east London later this month after serving part of his sentence for breaching his bail conditions.

He received a 50-week sentence after being found guilty of breaching his bail when he took refuge in the Ecuadorian embassy for several years.

Assange will stay in prison as he fights extradition to the US ( Reuters: Henry Nicholls )

A judge at the Westminster Magistrates' Court found there were substantial grounds to believe Assange would abscond again.

The Australian's remand status will change to that of a prisoner facing extradition.

The 48-year-old is fighting extradition to the United States over allegations he leaked classified government material.

AFP/ABC