Cuba's communist government says it has arrested dozens of dissidents who were in contact with the US representative in Havana.
Mr Cason is said to have openly met with Cuban dissidents
In an official statement read out on state television, the authorities accused the representative, James Cason, of "subversive" activities.
President Fidel Castro has made no secret of his dislike for Mr Cason - describing him last week as a "bully" and a "liar".
The Cuban Government also announced on Tuesday that it was restricting the movements of US diplomats, in response to similar measures imposed on Cuban diplomats in Washington.
The two neighbours have not maintained formal diplomatic relations for more than 40 years, but the US does have a limited diplomatic presence in Havana.
The arrests were the result of "the shameful and repeated attitude by the chief of Washington's diplomatic mission in Havana," the Cuban statement said.
The most intense wave of repression this year is under way
Cuban rights activist Elizardo Sanchez
It said the detainees would be put on trial.
Late on Tuesday, veteran Cuban rights activist Elizardo Sanchez said those arrested numbered up to two or three dozen.
"The most intense wave of repression this year is under way
right now," Mr Sanchez told the AFP news agency.
The arrests follow a souring of relations between Washington and Havana, after Mr Cason's arrival as the new head of Cuba's US interest section in September.
Mr Cason is currently the focus of something approaching a personal vendetta by the Cuban Government, the BBC Havana correspondent Stephen Gibb says.
He has irritated Mr Castro by stepping up US support for his opponents, and regularly meeting opposition members and journalists in his Havana residence, our correspondent says.
But Mr Cason has insisted his aim is to promote democracy and human rights.
"The Cuban Government is afraid - afraid of freedom of
conscience, afraid of freedom of expression, afraid of
human rights," he said during a meeting with opposition leaders last month.