HAVANA -- A politically recharged President Fidel Castro marked his 74th birthday Sunday, addressing a graduating class of health care workers and making a veiled reference to the recent defection to the United States of two medical workers who had been assigned to Zimbabwe.

``These Cuban health care workers will leave an indelible imprint as they travel around the world, providing their services and sowing medical schools in other lands,'' Castro said at the ceremony.

``Today, it gives us immense satisfaction to take part in the graduation of 4,000 new members of the glorious contingent of professionals who bring such honor to the homeland.''

The two Cuban medical workers who defected, Leonel Córdova Rodríguez, 31, and Noris Peña Martínez, 25 -- were granted U.S. refugee status and flew to Miami last week.

In the process of seeking asylum, they said, they were kidnapped by Zimbabwean security officers, who helped Cuban diplomats force them onto a flight to Havana. Air France refused to let them board during a stopover in South Africa after the doctors slipped a note to a crew member saying they were kidnap victims.

At the time, Cuba denied any involvement in the alleged kidnapping.

Without referring specifically to that case on Sunday, Castro criticized ``imperialist'' nations that ``offer money and make all kinds of promises to our doctors, hoping to bribe them into defection and treason, heedless of the lives that would be lost as a result.''

Other than greetings delivered to Castro by several speakers at the graduation, there was no public birthday celebration Sunday.