One of the first pictures of Cuban leader Fidel Castro taken after his gastro- intestinal surgery. AFP PHOTO - JUVENTUD REBELDE.CU

Castro said he was "happy" and vowed to fight for his health.

The world's longest-serving head of government had not been seen since he underwent emergency surgery on July 31 and ceded power to his brother Raul Castro, 75, the defense chief.

Neither Castro had been seen publicly since, fueling some speculation about the president's health.

With a message reading "I feel very happy", pictures in the Juventud Rebelde newspaper showed the revolutionary icon alert and in good spirits after the operation to halt gastrointestinal bleeding.

"To all of you who wished me health. I promise I will fight for it. ... The country is moving forward and will continue marching forward perfectly well," Castro added.

The Miami newspaper El Nuevo Herald reported that Castro underwent a colostomy.

And Castro sounded prepared for complications. "I urge everyone to be optimistic and at the same time always prepared for any bad news there may be," he added.

Though Castro postponed official celebrations for his 80th birthday until until December, the pictures were a pointed attempt to keep Castro centrestage.

In the images, Castro wore Cuban team colors -- a red-white-and-blue tracksuit jacket -- rather than his customary khaki fatigues.

Two pictures show him speaking on the phone.

Fidel Castro taken after his gastrointestinal surgery. AFP PHOTO - JUVENTUD REBELDE.CU

Another has him holding a copy of Saturday's copy of Granma, the communist party daily, with his own picture on the front page.

"For his 80th birthday, the commander-in-chief Fidel Castro sends a reassuring message about the state of his health, which has considerably improved," said Juventud Rebelde.

Russian President Vladimir Putin hailed Castro as one of the most "brilliant" political leaders of his era, in a special birthday message.

"In Russia, we know you well as one of the most brilliant and authoritative political men of current times," Putin said in a telegramme to the Cuban president, according to the Kremlin.

The United States, Castro's arch enemy for decades did not let up in its campaign against the president for his birthday.

"The Cuban people deserve the right to choose their own government," a US State Department spokesman, Justin Higgins, said in Washington.

Venezuelan President Hugo Chavez, a staunch ally whose country's oil has been key to keeping Cuba's economy afloat in recent years, was expected here to give Castro birthday greetings in person.

Castro has not been seen in public since July 26, the national holiday. Authorities announced on July 31 that he had temporarily ceded power to his brother because of the surgery.

It was the first time since the Cuban revolution in 1959 that he has officially ceded power, if only temporarily.

Details about Castro's health remain a secret but according to the state press, he is now walking and in good spirits.

An unidentified "friend" told the Granma newspaper in an article published Saturday that Castro was taking a few steps after therapy and conversing.

Cuban officials have insisted regularly over the past week that life in the Americas' only communist nation is "completely normal" as Castro recuperates.

After his surgery, Castro had asked that his birthday celebration be postponed until December 2, the 50th anniversary of his return from exile in Mexico to topple US-backed dictator Fulgencio Batista.

Yet a scaled-back birthday bash went on, with concerts and other events across the country.

A giant concert took place Saturday in Havana to honour Castro in what the government called "an expression of the people's strong and unified support for the revolution."

The concert was held outside the US Interests Section in Havana and lasted throughout the night. Singer-songwriter Amaury Perez orchestrated the soiree, which also featured musicians Frank Fernandez, Rosita Fornes and Kiki Korona, as well as the groups Hipnosis, Karma and Eddy K.

At midnight, the crowd of several thousand shouted: "Happy Birthday!", "Viva Fidel!, Viva Raul!"