The Norwegian police on Monday said Dutch investigators were helping them search for WikiLeaks founder Julian Assange's associate Arjen Kamphuis, who mysteriously disappeared in northern Norway three weeks ago.

The 47-year-old Dutch cyber security expert has been missing since August 20 when he left his hotel in the northern Norwegian town of Bodo, triggering numerous conspiracy theories on social media.

Two Dutch investigators have arrived in Bodo to help the investigation, the Norwegian police said in a statement on Monday, adding they would stay there for the rest of the week.