OTTAWA (Reuters) - Canadian officials have traveled to North Korea to discuss the case of a Canadian pastor serving a life sentence there, a spokesman for Prime Minister Justin Trudeau said on Tuesday.

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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.

The delegation is headed by Daniel Jean, Trudeau’s national security advisor.

“A Canadian government delegation is currently in Pyongyang to discuss Pastor Lim’s case,” Trudeau’s press secretary Cameron Ahmad said.

“His health and wellbeing remain of utmost importance to the government and we are obviously continuing to engage on his case and, given that it is an active case, we cannot provide any further comment at this time.”

Lim’s family has become more concerned for his welfare since the June death of American student Otto Warmbier who had been held in North Korea for 17 months. Warmbier died in a Cincinnati hospital just days after he was released in a coma. Canadian officials visited Lim in December 2016.

In addition to Canada’s Lim, North Korea is holding three Americans.

Lim’s Toronto-area church has said Lim visited North Korea more than 100 times since 1997 and helped set up an orphanage and nursing home.

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

The U.N. Security Council imposed new sanctions on North Korea at the weekend over its continued missile tests, and U.S. President Donald Trump on Tuesday warned the country would be met with “fire and fury” if it threatens the United Sates.