MEXICO CITY — Fidel Castro is resting and recovering from stomach surgery, top Cuban officials said Saturday, as the island beefed up security, saying it fears a U.S. attack during the Cuban president's health crisis.

Cuba's vice-president said Castro does not have stomach cancer and is recuperating well from surgery.

"He is coming along well. He does not have stomach cancer,'' Carlos Lage said during a visit to Bolivia for the opening of a constitutional assembly.

"He's been made well by the operation and is recuperating favourably.''

Cuban parliament Speaker Ricardo Alarcon also said in comments broadcast Saturday by CNN en Espanol that Castro "remains in stable condition'' and "is resting in order to recover as quickly as possible.'' The interview was taped late Thursday by state-run Cubavision International in a special package for CNN and was not previously aired.

Meanwhile, former revolutionaries -- most of them in their 60s and 70s and who defended against the failed U.S.-backed Bay of Pigs invasion in 1961 -- promised they would fight for Cuba in the event of a possible U.S. attack.

Under the control of Castro's brother, Defence Minister Raul Castro, the Cuban government has mobilized citizen defence militias and asked military reservists to check in daily.

The Communist Party daily newspaper Granma published a statement by the Association of Combatants of the Cuban Revolution on its front page, telling Fidel Castro: "We will continue working with the same revolutionary fervour that you taught us.'' The veterans' group also expressed confidence that Castro would be back on his feet soon.

In Washington, the White House has insisted no invasion threat exists, with press secretary Tony Snow dismissing the suggestion that the United States would attack the island as "absurd.''   

The newspaper also filled its front page with emotional messages from top Cuban cultural figures like folk singer Pablo Milanes and Juan Formell, the director of Los Van Van, one of the island's most popular tropical groups.

"This is a delicate moment and it's necessary to prepare, because the enemy might have illusions,'' Formell said from Japan. "I trust in our Armed Forces, and in our people.''

Milanes, also travelling outside Cuba, said he promised to represent Castro and the Cuban people "as this moment deserves: with unity and courage in the presence of any threat or provocation.''

Neither of the Castros has been seen since Monday's announcement that Fidel, 79, had undergone surgery and was temporarily ceding power to Raul, 75. No new details were provided on Castro's condition following the surgery for intestinal bleeding.

The Bush administration rejected the idea that it would take advantage of Castro's illness to attack the island.

"The U.S. has absolutely no designs on invading Cuba,'' Snow said in Crawford, Texas, where U.S. President George W. Bush was vacationing at his ranch. "Cubans are going to have to chart their destiny. It's the one thing that they've been deprived (of) during the dictatorship of Fidel Castro.''

Some Cuban exiles, seizing on the unprecedented transfer of power, called for the U.S. government to do more to encourage a democratic transition on the island.

William Sanchez, a lawyer for the Cuban-American non-profit Democracy Movement, urged Bush to tell Cuba to set an elections timetable and let Cuban-Americans come to the island to help with a political transition.

The Cuban government used such statements by what it calls the "terrorist mafia'' in Miami -- as well as Bush's call Thursday for democratic change on the island -- to justify its fears of an invasion.