OTTAWA (Reuters) - The Canadian Liberal government, criticized by opposition legislators for sending a patrol ship to Havana while Russian vessels were there, on Monday said the visit was meant to send a message of deterrence to Moscow.

The Canadian navy patrol ship sailed into the harbor early on Friday, two days after the arrival of a Russian nuclear-powered submarine and a frigate. Canada and the United States said they were closely monitoring the vessels.

"The deployment ... sends a very clear message that Canada has a capable and deployable military and we will not hesitate to do what is required to protect our national interest," Defence Minister Bill Blair told reporters.

"Canadian Armed Forces will continue to track the movements and activities of the Russian ships," he added. "Presence is deterrence. We were present."

Both the U.S. and Cuba say the Russian warships pose no threat to the region. Russia has also characterized the arrival of its warships in allied Cuba as routine.

Canada has traditionally been one of Cuba's closest Western allies and maintained ties after the 1959 Cuban revolution. Relations though tend to be better under Liberal governments, since the official opposition right-of-center Conservatives are more staunchly anti-Communist.

"Why is the Trudeau government sending a Canadian warship to 'celebrate' relations with a communist dictatorship at all - let alone while Russian warships are docked there? Cuba and Russia are not allies of Canada," Conservative foreign affairs spokesman Michael Chong said in a social media post.

Prime Minister Justin Trudeau paid an official visit to Cuba in November 2016. When former leader Fidel Castro died a few days later, Trudeau referred to him as a "remarkable leader", prompting Conservative unhappiness.

(Reporting by David Ljunggren; Editing by Bill Berkrot)