Cuba's communist government announced Tuesday night it had rounded up several dozen opponents and confirmed new restrictions on U.S. diplomats amid worsening relations between the two countries.

An official statement on state television accused the chief of Washington's diplomatic mission in Havana, James Cason, of trying "to foment the internal counterrevolution."

The statement continued: "No nation, no matter how powerful, has the right to organize, finance and serve as a center for subverting the constitutional order."

Offices at the U.S. Interests Section were closed late Tuesday and attempts to reach American diplomats were unsuccessful. The U.S. State Department last week had reported the travel restrictions on its diplomats in Havana, but the Cuban government did not confirm the new measures until Tuesday.

In Washington, a State Department official said they had not seen the announced measures but would look into them.

Havana's actions are just the latest in an increasingly ugly exchange of words between the two governments, which have had no regular diplomatic relations for more than four decades.

The announcement said several dozen government opponents had been detained but did not elaborate or say if any charges pending.

Veteran human rights activist Elizardo Sanchez said by telephone late Tuesday that he had confirmed the detentions of at least 10 dissidents and was checking on reports of another 20 or so picked up by state security agents.

Havana in recent weeks has become increasingly incensed with Cason, who last month made a high-profile visit to a meeting of dissidents and spoke with international journalists gathered there.

Since arriving here about six months ago, Cason has met with opposition members around the island and last week allowed a group of dissident journalists to use his official residence for a meeting.

Cason has said he is merely trying to promote democracy and human rights in the Caribbean nation.

"The Cuban government is afraid -- afraid of freedom of conscience, afraid of freedom of expression, afraid of human rights," Cason told journalists during last month's meeting with the opposition.

President Fidel Castro responded shortly thereafter by criticizing Cason's public appearance and comments. "Anyone can see that this is a shameless and a defiant provocation," he said.

The U.S. State Department then called Castro's criticisms of Cason "derogatory."

The U.S. State Department last week announced it was restricting the freedom of travel of Cuban diplomats in the United States, responding to curbs imposed by Havana on U.S. officials in Cuba.

American government sources said they believe the Cuban government made the first move as a means of cutting back on Cason's extensive travels across the island.

Cuban officials have also become increasingly upset about a new solitary confinement lockdown on five convicted Cuban spies serving time in American prisons.

The five were convicted in Miami of trying to infiltrate U.S. military bases and Cuban exile groups in Florida. Their sentences range from 15 years to life.

Cuban authorities have lionized the men as patriotic heroes and say they were merely working to prevent Cuban exile groups from launching terrorist acts against their homeland.