The arrests were an "appalling act of intimidation", the US said

State Department spokesman Richard Boucher said Washington was "outraged" by the detentions.

"This is an appalling act of intimidation against those who seek freedom and democratic change in Cuba," Mr Boucher said.

He also strongly defended the US envoy, James Cason, against Cuban accusations of carrying out subversive activities.

Relations plummet

Mr Boucher called on the United Nations Human Rights Commission, which opened its annual meeting in Geneva on Monday, to censure Cuba for the arrests.

"These people have been arrested for simply speaking out, one of the most basic internationally accepted human rights," he said.

The arrests by Cuba have sent relations between the Cold War rivals plummeting again.

On Tuesday, an official statement on Cuban television accused Mr Cason of trying "to foment the internal counterrevolution".

"No nation, no matter how powerful, has the right to organise, finance and serve as a centre for subverting the constitutional order," it said.

Cuban President Fidel Castro has made no secret of his dislike for Mr Cason - describing him last week as a "bully" and a "liar".

Cuba also announced on Tuesday it was restricting the movements of US diplomats, in response to similar measures imposed on Cuban diplomats in Washington.

It said the detainees would be put on trial.

'Intense repression'

The non-governmental group Reporters Without Borders said at least a dozen of those arrested were independent journalists.

Mr Cason is said to have pursued meetings with Cuban dissidents

Veteran human rights activist Elizardo Sanchez said the detentions represented "the most intense repression in recent years".

The arrests follow a souring of relations between Washington and Havana after Mr Cason's arrival as the new head of Cuba's US interests section in September.

He has stepped up US support for opponents of the Castro regime and regularly meets opposition members and journalists in his Havana residence.

Mr Cason insists his aim is to promote democracy and human rights.

Mr Boucher backed his actions, saying: "The activities of our diplomats in Cuba are similar to the activities we carry out around the world.

"This response by Cuba is a response to the growing opposition movement on the island and the increasing desire of change among the population," he said.