Mr Farinas says he is not seeking to overthrow the government
Cuba says it will not be "blackmailed" by a dissident journalist who is on hunger strike to seek the release of ailing political prisoners.
Guillermo Farinas, 48, began his action after Orlando Zapata Tamayo died while on hunger strike in jail.
Communist Party newspaper Granma, which reflects government policy, said it would not bow to pressure.
It said Western media were "calling attention to a prefabricated lie" by reporting his case.
"Cuba, which has demonstrated many times its respect for human life and dignity, will not accept pressure or blackmail," the newspaper said.
Mr Farinas says he will continue to refuse food and water until the Cuban authorities release the country's 26 most vulnerable and ailing political prisoners.
He has said he is not seeking the overthrow of the government or greater freedom of expression in the country.
"I say to them - either they free the 26 political prisoners who are sickest, or nothing. I am going to stick to my position to the end," he told AFP news agency.
Some 43 Cuban political prisoners released a statement in support of his protest, saying they were "profoundly touched" by his sacrifice, AFP said.
But Granma said Mr Farinas was "an agent in the service of the United States", Cuba's foe and added: "It is not medicine that must resolve a problem created with the intent to discredit our political system but the patient himself and the stateless people, foreign diplomats and the media who manipulate him".
Mr Farinas began his strike on 24 February, a day after Zapata died following an 85-day hunger strike to protest at prison conditions.
The case of Zapata, whom human rights campaign group Amnesty International declared a prisoner of conscience, drew widespread international condemnation and calls for the release of all Cuba's detained political dissidents.
His death marked the first time in nearly 40 years that a Cuban activist had starved himself to death to protest against government abuses.
Cuba's illegal but tolerated Human Rights Commission says there are about 200 political prisoners still held in Cuba, about one-third less than when Raul Castro took over as president from his brother Fidel.