MOMBASA, Kenya: Undeterred by US and French hostage rescues that killed five bandits, Somali pirates brazenly hijacked four 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 deaths of their colleagues - and the top US military officer said yesterday he takes those comments seriously. But Admiral 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."

Still, despite Mullen's confident statement and President Barack Obama's warning on Monday, pirates captured two more nautical trophies yesterday to match the two ships they seized a day or two earlier.