Somali pirates hijacked two more cargo vessels and opened fire on two others on Tuesday in attacks that showed a determination to go on striking at shipping on the region's strategic trade routes. The capture of the Greek-owned MV Irene E.M. and Togo-flagged MV Sea Horse were a clear sign pirate gangs have not been deterred by two raids in recent days in which U.S. and French special forces have killed five pirates. NATO Lieutenant Commander Alexandre Fernandes said the Portuguese warship Corte-Real had received a pre-dawn distress call from the St. Vincent and the Grenadines-flagged Irene E.M. as it traveled through the Gulf of Aden. "There was only three minutes between the alarm and the hijack," Fernandes told aboard the warship. "They attacked at night, which was very unusual. They were using the moonlight as it's still quite bright." Greece's Merchant Marine Ministry said the Irene E.M.'s 22 crew were Filipinos. The East African Seafarers' Assistance Program, which tracks piracy, said they were all unharmed. The bulk carrier was sailing from Jordan to India. Its Piraeus-based owners were not immediately available for comment. Hours later, NATO officials on the Corte-Real said the nearly 5,000-tonne MV Sea Horse had also been seized about 77 nautical miles off Somalia. It was hijacked by pirates on board three or four skiffs, they said. The officials said another pirate gang fired automatic rifles and rocket-propelled grenades at the Liberian-flagged 21,887-tonne Safmarine Asia. They said it managed to escape and that there was no word of any casualties. The U.S.-flagged cargo ship Liberty Sun also was attacked by pirates firing rocket-propelled grenades and automatic weapons, the ship's owner, New York-based Liberty Maritime Corp, said in a statement. The pirates damaged the ship but did not manage to board it. Liberty Sun immediately requested help from the U.S. Navy and is now under escort. The ship was carrying U.S. food aid and headed to Mombasa, Kenya, from Houston.