North Korea have freed a Canadian pastor who was serving a life sentence there on humanitarian grounds, just hours after the United States warned it would counter any threat from the North with "fire and fury".

The release came a day after Canadian officials said a delegation led by the country's national security adviser had traveled to North Korea to discuss the case of Hyeon Soo Lim, sentenced to hard labor for life in December 2015.

North Korea had accused Lim, who served in one of the largest churches in Canada, of attempting to overthrow the regime.

"Rim Hyon Su, a Canadian civilian, was released on sick bail according to the decision of the Central Court of the DPRK on August 9, 2017, from the humanitarian viewpoint," said North Korea media

There was no obvious direct connection between the release and the standoff with the United States, but North Korea has in the past attracted the attention of Washington, and visits by high-profile Americans, with the detention and release of U.S. citizens.