Diplomats from Canada this week paid a rare visit to North Korea and were able to see a Canadian pastor serving a life sentence for subversion, a foreign ministry official said.

Hyeon Soo Lim, who served at one of the largest churches in Canada, was sentenced to hard labor for life in December 2015 for what North Korea says was an attempt to overthrow the regime.

Chantal Gagnon, a spokeswoman for Canadian Foreign Minister Stephane Dion, confirmed a report by North Korea's KCNA news agency that said the diplomats visited the country from Tuesday until Thursday and saw Lim.

"We are still very concerned about his health, well-being and continued detention and are ‎working actively to secure his release," she said.

"This case is absolutely a priority for us," she added, declining to give details of Lim's health.

In a statement, Lim's Toronto-area church said "we are hopeful that this is a positive sign that we will see Reverend Lim released and home soon."

Canada established diplomatic relations with Pyongyang in 2001 but froze them in 2010. Ottawa now says it will only talk to North Korea about regional security, human rights and consular cases.

The church has said Lim visited North Korea more than 100 times since 1997 and helped set up an orphanage and nursing home.

In January, Lim told CNN he spends eight hours a day digging holes at a labor camp where he has not seen any other prisoners.