"The presence of a nuclear submarine there at this moment makes it imperative to wonder what is the military reason behind this action in this peaceful region of the world," Cuba's foreign ministry said in a statement. Washington did not confirm that there was a submarine at the naval base.

The ministry did not specify whether the submarine was armed. It said it was at the base from July 5 to July 8.

The U.S. State Department declined to give information about movements of military assets. It said Cuba was looking to distract from the two-year anniversary of largest street protests seen in Cuba since Fidel Castro's 1959 revolution. On Monday, Cuba had accused the U.S. of inciting that unrest.

"Attempts by the Cuban government to distract the world from the significance of this day are transparent and risible," a State Department official said.

The White House and U.S. Department of Defense did not immediately respond to requests for comment.

William LeoGrande, a professor at Washington's American University, told Reuters it was hard to know the motivation for the submarine's movements, pointing to possible technical problems or a response to recent worries about China.

"Overall this is an incident that is really a symptom of the fact that Cuba has once again become caught between superpowers in what appears to be the emergence of a new Cold War," he said.

Cuba has long called for the U.S. to close its 121-year-old naval base on the eastern part of the island, along with the military prison Washington established there in 2002.

Critics have said the Guantanamo Bay prison has been used for arbitrary detention and torture of people suspected of terrorism.

In June, Havana and Beijing rejected reports citing U.S. officials alleging that China was using Cuba as a spy base. The United States has presented no evidence of such a base.

Tuesday's ministry statement warned of the dangers of circulating nuclear submarines and armed forces across the Caribbean, adding that a history of U.S. military bases across the region threatened its peoples' sovereignty.

The ministry also reiterated calls for the United States to end its military presence on the island, saying this served only to "outrage Cuba's sovereign rights" and carry out acts of detention, torture and the systemic violation of human rights.

It added that U.S. military leaders have made public plans to use their "war capabilities" to realize U.S. ambitions over the region's natural resources.

The U.S. has maintained a trade embargo against the Caribbean island for more than 60 years.

During an economic crisis aggravated by the COVID-19 pandemic, tens of thousands of Cubans have emigrated to the United States.