WASHINGTON (CNN) -- President Bush announced Wednesday night he has ordered the coalition attack on Iraq to begin.
"American and coalition forces are in the early stages of miltary operations to disarm Iraq, to free its people and to defend the world from grave danger," Bush said.
He said the first strikes were against "selected targets of military importance."
The attack in Iraq early Thursday morning, involving F177A Stealth fighters and multiple cruise missiles from U.S. warships, was a "decapitation attack" to take out Iraqi President Saddam Hussein even before the planned start of the war, Pentagon sources told CNN.
Whether the mission succeeded is not known. Administration officials told CNN the strike was ordered for fear the opportunity could be lost.
Air raid sirens were heard in Baghdad at about 5:30 a.m. Thursday (9:30 p.m. Wednesday ET) about 90 minutes after the U.S. deadline for Iraqi President Saddam Hussein to step down or face a U.S.-led military attack.
In his four-minute announcement from the Oval Office, Bush said the military campaign, supported by 35 nations, would make efforts to spare Iraqi civilians. But he made it clear the U.S. military planned to use its full might in the war.
"This will not be a campaign of half measures, and we will accept no outcome except victory," he said.
The president's address came at 10:15 p.m., about two hours and 15 minutes after the expiration of a deadline he set for Iraqi leader Saddam Hussein and his sons to leave the country or face military action.
The United States and Britain have massed nearly 300,000 troops in the Persian Gulf region.
Earlier, Adm. Timothy Keating, commander of the U.S. 5th Fleet, said allied forces were prepared to carry out an "unprecedented" campaign: "If we go, the plans we have are unlike anything anyone has ever seen before."
In the hours leading up to the deadline, about a dozen U.S. and coalition warplanes dropped precision munitions on nearly a dozen Iraqi artillery pieces in the southern no-fly zone that could have been in range of American troops poised to invade southern Iraq, Pentagon officials told CNN.
There was also concern some of the artillery could be capable of using chemical weapons and U.S. planes had been conducting around-the-clock reconnaissance of the sites.
Warplanes also struck Iraqi cable repeater sites and command and control sites. In addition, at least one Al Ababil surface-to-surface missile launcher was struck.