Suspected suicide bombers blasted a hole in a US Navy destroyer in a Yemeni port yesterday, killing six American sailors and leaving 11 missing.
Navy officials said about 35 others on board were injured, five seriously, when an explosives-laden boat blew up near the USS Cole, one of the world's most advanced guided missile destroyers.
The vessel, which had been on a refuelling stop in Yemen's southern port, Aden, was left listing and with a six-by-12 metre gash along its waterline.
"If, as it now appears, this was an act of terrorism it was a despicable and cowardly act. We will find out who was responsible and hold them accountable," President Bill Clinton said.
"If their intention was to deter us from our mission of promoting peace and security in the Middle East, they will fail utterly."
The Pentagon ordered all US ships docked in the region to put to sea last night as a precaution against any further attacks.
The attack came amid mounting anti-US sentiment in much of the Arab world, including Yemen, over Washington's perceived support for Israel during two weeks of fierce Israeli-Palestinian violence.
US officials said reports from the scene indicated that two men aboard a small boat that had been assisting the Cole with mooring lines in the Aden harbour had stood to attention just before the blast destroyed their boat and holed the ship.
"This is looking more and more like terrorism," a senior Defence Department official said. "Of course, you can't confirm anything without a full investigation - but that's what it looks like - deliberate murder."
Attorney General Ms Janet Reno said that the US Bureau of Investigation was sending experts to Aden to help the Defence Department and other agencies to investigate the blast.
The explosion was so powerful that it blew windows out of buildings and sent terrified Aden residents fleeing into the streets. "Buildings shook as if the city had been hit by an earthquake," one witness said. The US Secretary of State, Ms Madeleine Albright, said the United States would not be cowed by the attack.
"We will continue taking every step we can to protect our troops and our diplomats but we will not retreat from our responsibilities," Ms Albright said.
She said Washington would take all measures to protect its people, but added: "It does not mean we can crawl into an ostrich-like mode. We are eagles."
The attack on the warship came on the same day that Israeli helicopter gunships blasted Palestinian targets in the West Bank and Gaza Strip with missiles to avenge the killing of two Israeli soldiers by a lynch mob.
A navy spokesperson, Lieut Meghan Mariman, said in Washington that the crew of the Cole was trying "very hard to keep the ship afloat", adding that the vessel was carrying about 300 people.
The last major attack on US targets was in August 1998 when twin bombs at the US embassies in Kenya and Tanzania killed more than 250 people.
Yemeni President Mr Ali Abdullah Saleh offered his condolences to Mr Clinton and the "friendly American people", but said he believed the explosion was not caused by a deliberate act.
State-run Yemeni television showed Mr Saleh visiting the wounded sailors at a local hospital and said he spoke by telephone to Ms Albright to assure her that Sanaa was investigating the blast.
Yemen has been plagued by generally low-level terrorism for many years. Following the Afghan war, many Muslim fighters took refuge there, taking advantage of lax security, the ready availability of weapons and the rugged terrain to use it as a base for training and activities in other countries.
The Arleigh Burke Class destroyer Cole is one of the world's most sophisticated warships.
The 154-metre-long Cole is equipped with an advanced Aegis radar defence and with missiles and guns to protect itself and aircraft carrier battle groups against simultaneous attack by planes, missiles and ships.
Lieut Terrence Dudley from the Fifth Fleet said: "USS Cole has been stabilised and the flooding has been contained. Luckily there have been no fires."