MOMBASA, Kenya Undeterred by U.S. and French hostage rescues that killed five bandits, Somali pirates brazenly hijacked three more ships in the Gulf of Aden, the waterway at the center of the world's fight against piracy.

Pirates have vowed to retaliate for the killing of their colleagues and the top U.S. military officer said today he takes those comments seriously.

But Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, told ABC's "Good Morning America" that "we're very well prepared to deal with anything like that."

The latest trophy for the pirates was the M.V. Irene E.M., a Greek-managed bulk carrier sailing from the Middle East to South Asia, said Noel Choong, who heads the International Maritime Bureau's piracy reporting center in Kuala Lumpur.

The Irene was attacked and seized in the middle of the night a rare tactic for the pirates.

U.S. Navy Lt. Nathan Christensen, spokesman for the Bahrain-based 5th Fleet, said the Irene was flagged in the Caribbean island nation of St. Vincent and the Grenadines and carried 23 Filipino crew. Choong reported a crew of 21, and there was no immediate way to reconcile the figures.

A maritime security contractor, speaking on condition of anonymity because it is a sensitive security issue, said the ship put out a distress signal "to say they had a suspicious vessel approaching. That rapidly turned into an attack and then a hijacking."

On Monday, Somali pirates also seized two Egyptian fishing boats in the Gulf of Aden off Somalia's northern coast.