NAIROBI, Kenya – NATO says Somali pirates have hijacked another cargo ship in the Gulf of Aden, the fourth ship seized in the last two days. NATO spokeswoman Shona Lowe says the Lebanese-owned MV Sea Horse was attacked Tuesday off the Somali coast by pirates in three or four speedboats. She had no further details. Earlier, Somali pirates captured the MV Irene E.M., a Greek-managed bulk carrier sailing from the Middle East to South Asia. The Irene was seized in the middle of the night Tuesday — a rare tactic for the pirates. Somali pirates appear undeterred by U.S. and French attacks that have killed five pirates in the past week during hostage rescues, including that of an American sea captain. Pirates have vowed to retaliate for the killing of their colleagues. THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below. MOMBASA, Kenya (AP) — 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 Tuesday 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 Tuesday — 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." "They tried to call in support on the emergency channels, but they never got any response," the contractor said. On Monday, Somali pirates also seized two Egyptian fishing boats in the Gulf of Aden off Somalia's northern coast, according to Egypt's Foreign Ministry, which said the boats carried 18 to 24 Egyptians total. A flotilla of warships from nearly a dozen countries has patrolled the Gulf of Aden and nearby Indian Ocean waters for months. They have halted several attacks on ships this year, but say the area is so vast they can't stop all hijackings. Choong said pirate attacks this year had risen to 77, with 18 of those ships hijacked and 16 vessels with 285 crew still in pirates' hands. Each boat carries the potential of a million-dollar ransom. The latest seizures come after Navy SEAL snipers rescued American ship captain Richard Phillips on Sunday by killing three young pirates who held him captive in a drifting lifeboat for five days. A fourth pirate surrendered after seeking medical attention for a wound he received in trying to take over Phillips' vessel, the Maersk Alabama. Phillips is aboard a Navy vessel at an undisclosed location, Christensen said Tuesday. He was initially taken aboard the Norfolk, Va.-based USS Bainbridge and then flown to the San Diego-based USS Boxer for a medical exam. In Washington, President Barack Obama appeared to move the piracy issue higher on his agenda, vowing the United States would work with nations around the world to fight the problem. "I want to be very clear that we are resolved to halt the rise of piracy in that region and to achieve that goal, we're going to have to continue to work with our partners to prevent future attacks," Obama said at a news conference Monday. The 19 crew members of the Alabama celebrated their skipper's freedom with beer and an evening barbecue Monday in the Kenyan port of Mombasa, said crewman Ken Quinn. The vessel's chief mate was among those urging strong U.S. action against piracy. "It's time for us to step in and put an end to this crisis," Shane Murphy said. "It's a crisis. Wake up." The U.S. is considering new options to fight piracy, including adding Navy gunships along the Somali coastline and launching a campaign to disable pirate "mother ships," according to military officials. They spoke on condition of anonymity because no decisions have been made yet. In Burlington, Vt., Phillips' wife, Andrea Phillips thanked Obama, who approved the dramatic sniper operation. "With Richard saved, you all just gave me the best Easter ever," she said in a statement. The four pirates that attacked the Alabama were between 17 and 19 years old, Defense Secretary Robert Gates said. "Untrained teenagers with heavy weapons," Gates told students and faculty at the Marine Corps War College. "Everybody in the room knows the consequences of that." U.S. officials were now considering whether to bring the fourth pirate, who surrendered shortly before the sniper shootings, to the United States or possibly turn him over to Kenya. Both piracy and hostage-taking carry life prison sentences under U.S. law. The French navy late Monday handed over the bodies of two Somali pirates killed in a hostage rescue operation last week to authorities in Somali's semiautonomous northern region of Puntland and locals buried the bodies.