Canada is extending the anti-piracy mission of HMCS Winnipeg off the coast of Somalia, Defence Minister Peter MacKay told CTV's Question Period Sunday.

MacKay said the federal government agreed to a NATO request for the frigate to continue operations as part of an allied effort to deter pirates who have seized dozens of vessels off the Horn of Africa.

The defence minister said the mission would be extending "into June," and possibly longer.

"These dates are fluid as a result of the requirements and the sailing time. Certainly the families we wanted to notify first, wanted to let them know that this time will be a little bit further into the summer," MacKay said.

Responding to questions why pirates were being released, MacKay said it was because they are operating in a "flux zone" outside of territorial limits of coastal countries and therefore not subject to international law. But he said Canada is pursuing other legal avenues to prosecute the pirates.

"Canada is currently in the midst of very aggressively seeking an agreement so that Canada will in fact be able to arrest and have individuals charged and put ashore in certain countries where trials can occur."

He noted that several NATO allies such as the United States, France and Britain already have agreements with some African countries that allow for prosecutions on their soil.

Marc Isaacs, a lawyer specializing in maritime law, disagreed with MacKay and told CTV Newsnet that Canada does have jurisdiction to detain pirates under the UN Law of the Sea convention.

"Piracy laws are also on the books here in Canada. The Criminal Code of Canada makes piracy an offence, whether committed in Canada or outside Canada," he added Sunday evening.

Isaacs said he didn't understand why Canada was releasing detained pirates.

"At the very least the pirates should be detained and turned over to the flag state of the vessel they were attacking," he said.

MacKay also praised the work of Canadian sailors aboard the Winnipeg who have been instrumental in preventing several attacks.

"Our men and women there are acting extremely courageously in deterring the piracy attacks. We have at least three if not more attempts that have been made where HMCS Winnipeg has intervened and prevented those attacks," he said.