Cuba's military is trying to send a message to the U.S. that, although its uniformed ranks are depleted, Cubans are prepared to fight to defend the island nation, says a Canadian expert on the country.

Hal Klepak, a historian at the Royal Military College of Canada in Kingston, Ont., said Cuba is on high alert for internal disturbances out of fear they could be fuelled by the U.S. in an effort to topple the U.S. government.

In Cuba for research, Klepak made the comments after Cuba's armed forces recently paraded through the streets of Havana in a display of military force.

Klepak said the military is down to its bare bones.

"It is essential that the Cuban armed forces show that this will not be quick victory," Klepak said.

The Cubans realize they can't win an all-out war against the United States, he said, but "they will still be in a position to make the war long, bloody, costly and embarrassing.

"They believe and they are determined."

On Sunday, a crowd of government supporters swarmed a small group of dissidents in the Cuban capital Havana.

The demonstrators were on a silent march in a Havana park to mark International Human Rights Day when they were roughed up.

It was one of the first public confrontations since President Fidel Castro disappeared from public life because of illness in July.

Loyalists accused Sunday's demonstrators of being mercenaries for the U.S. government.

Klepak said that during the past four months, with Castro sick and out of the public eye, the U.S. has been trying everything short of armed invasion to find chinks in Cuba's self-defence plan.

When Cuba's economy nearly collapsed after the fall of the Soviet Union in the early 1990s, the country drastically cut its armed forces to about 55,000 from 300,000 troops.

If it had to muster a real fighting force, Klepak said the Cuban military would need the "people's army," hundreds of thousands of trained civilians on the reserve list, to put up a real fight. Klepak estimated there are 700,000 trained reservists in Cuba.

With files from the Associated Press