North Korean state media says Australian student Alek Sigley was caught committing spying acts which led to his expulsion.

Key points: North Korea's KCNA newsagency accused Mr Sigley of passing on data and photographs to "anti-DPRK" media

North Korea's KCNA newsagency accused Mr Sigley of passing on data and photographs to "anti-DPRK" media It said Mr Sigley had admitted his "spying acts" prior to being expelled

It said Mr Sigley had admitted his "spying acts" prior to being expelled Mr Sigley was released by North Korea following the intervention of a Swedish envoy

Mr Sigley was released by North Korea on Thursday after the intervention of a Swedish envoy and flew to Tokyo where he re-joined his wife.

He has since said he would not be commenting on the circumstances of his detention in North Korea.

But North Korea's KCNA newsagency said he collected data and photographs that he passed on to "anti-DPRK" media outlets.

It said Mr Sigley was caught "red-handed" by a "relevant institution" of the North on June 25 and had abused his status as a student.

The newsagency said he admitted his "spying acts" and repeatedly asked for a pardon and was expelled from the country out of "humanitarian leniency."

"He honestly admitted his spying acts of systematically collecting and offering data about the domestic situation of the DPRK and repeatedly asked for pardon, apologising for encroachment upon the sovereignty of the DPRK," the agency said.

The country had not commented on Mr Sigley prior to the newsagency's reports on Saturday.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 15 seconds 15 s Alek Sigley touches down in Japan after release from North Korean detention

During his time in North Korea, Mr Sigley often shared details about his life in Pyongyang through social media and the website of his travel agency, Tongil Tours, frequently challenging negative outside perceptions about the North and reporting of the extraordinary freedom he had as one of the few foreign students living there.

Mr Sigley had been studying at a Pyongyang university and guiding tours in the North Korean capital before disappearing from social media contact with family and friends.

He also wrote opinion articles and essays that appeared in Western media, such as NK News.

His latest post on the NK News website, uploaded on April 30, described his dining experiences in Pyongyang.

"The six articles Alek published represent the full extent of his work with us and the idea that those columns, published transparently under his name between January and April 2019, are 'anti-state' in nature is a misrepresentation which we reject," Chad O'Carroll, CEO of NK News publisher the Korea Risk Group, said in a statement.

"Alek Sigley's well-read columns presented an apolitical and insightful view of life in Pyongyang which we published in a bid to show vignettes of ordinary daily life in the capital to our readers."

North Korea has been accused in the past of detaining Westerners and using them as political pawns to gain concessions.

Mr Sigley's father, Gary Sigley, a professor of Asian studies at the University of Western Australia, said his son was treated well in North Korea.

ABC/wires