Alek Sigley says he was forced to sign a false confession while held in North Korea. (AFP/NICOLAS ASFOURI)

An Australian student arrested for spying and expelled from North Korea last year said he was forced to write a false confession while held incommunicado.

Alek Sigley was studying modern Korean literature at Kim Il Sung University in Pyongyang when he went missing in June, sparking international alarm.

Canberra has no diplomatic representation in Pyongyang and turned to Sweden, the protecting power for its citizens.

Stockholm sent an envoy and Sigley was released after nine days in detention ― a much shorter period than some foreigners arrested in the authoritarian North.

Sigley had written articles for a number of publications while in Pyongyang and North Korean authorities accused him of espionage, saying they released him on grounds of "humanitarian forbearance". Writing in South Korean academic journal Monthly North Korea, Sigley said he was forced to admit guilt during an "unpleasant" nine-day interrogation "completely cut off from the outside world".