Norwegian authorities have begun to look into the credentials of a foreign media team who have been granted an interview by the man who has admitted to the deadliest attacks in the country since World War II, news reports said Tuesday, January 31.

Anders Behring Breivik has admitted to detonating a bomb in a government district in Oslo that killed eight people on July 22 and later shooting dead 69 others at a Labour Party summer camp on an island near the capital.

Goran Nilsson, deputy head of the prison where Breivik is held in custody, declined to name the media outlet or what country it was from, news agency NTB said, while public broadcaster NRK said it was a TV station.

Breivik has since January 9 been allowed to receive visitors under strict supervision, but according to Nilsson no members of Breivik's family or friends have applied to visit him.

At the same time he was granted access to newspapers and other media, and allowed to read letters sent to him while he was in isolation.

Defence attorney Geir Lippestad said he had advised Breivik not to conduct any interviews prior to the pending trial set to open April 16.

Thirty-two-year-old Breivik is due to face a new custody hearing next week, M&C reported quoting DPA.