An Australian student who was briefly detained in North Korea last year over spy charges says he had been kidnapped by secret police and forced to make a false confession, according to an article written by him and seen by Reuters.

Alek Sigley was held for nine days from June 25 while studying for a postgraduate degree in modern Korean literature at the prestigious Kim Il-sung University in Pyongyang, the North Korean capital.

He was expelled from the country after Swedish officials helped broker his release.

North Korean state media KCNA said he had admitted his "spying acts" including passing data and photos he collected by utilising his status as a foreign student to "anti-state" media outlets.

"I was innocent but they filed false charges against me,"

Beyond denying that he was a spy and saying he was sad to have lost access to North Korea, Sigley has not previously publicised details of his detention.

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In his first-hand account carried by a South Korea magazine, Sigley said that what appeared to be agents from the Stasi-like State Security Department, known as bowibu, "kidnapped" him from his dorm at the university.

"I was innocent but they filed false charges against me," he wrote, without elaborating.

"They endlessly tried to teach me some kind of lessons by forcing me to make a written confession which was a concoction of fabricated evidence and crimes and illogical legal reasonings."

"They succeeded in teaching me one lesson: the falsehood of the North Korean legal system,"

Sigley said on Twitter on Wednesday he had avoided speaking directly to the media in favour of telling his story "in my own words".

The article was printed in North Korea Monthly, published by the Seoul-based North Korea Research Institute, and included stories from his childhood and details about the lives of international students in North Korea.

During his detention, Sigley said he had "no idea" when he would be released because he was "completely cut off" from the outside world, while Australian officials were scrambling to secure his freedom with other countries.

"They succeeded in teaching me one lesson: the falsehood of the North Korean legal system," he said.

During his time in North Korea, Sigley had published articles about daily life for NK News and other specialised websites.

Reuters