Preliminary reports indicated the U.S.-led coalition was aiming at "targets of opportunity." It is not believed to be the main attack on Iraq.
President Bush is going to speak at 10:15 p.m.
The strike occurred hours after Mr. Bush's deadline for Saddam Hussein to surrender power passed unheeded.
As the 8 p.m. ET deadline passed, President Bush was in the living room of the White House residence. He received a phone call from his chief of staff Andrew Card, who informed Mr. Bush that neither the CIA nor the National Security Council had any evidence that Saddam Hussein had left Iraq - as demanded. White House spokesman Ari Fleischer said it means "the disarmament of the Iraqi regime will begin at a time of the president's choosing."
Weather could cause a delay or the Iraqis could start shooting first, but if everything remains on schedule, CBS News National Security Correspondent David Martin reports we are now 24 to 48 hours away from the start of the final battle with Saddam.
Tens of thousands of U.S. and British forces were massing at the Iraqi border in anticipation of an invasion that could begin at any moment. Other developments included:
Retired Lt. Gen Buck Kernan told CBS News Anchor Dan Rather, the military will likely strike immediately if they get intelligence that the Iraqis are preparing an attack. In the meantime, the U.S. coalition is still poised to take advantage of Turkish airspace if that country's parliament grants permission in a vote expected early Thursday.
Near the front lines, long lines of U.S. tanks, Bradley fighting vehicles and fuel trucks snaked through the Kuwaiti desert in columns, fighting sandstorms. U.S. and British troops piled ammunition and combat gear into fighting vehicles and broke camp, ready to invade on short notice.
In all, about 300,000 troops were within striking distance of Iraq, backed by more than 1,000 warplanes.
Seventeen Iraqis walked across the border into Kuwait and surrendered Wednesday – the first in what is expected to be a flood tide of Iraqi soldiers who come out with their hands up once the shooting starts. The air campaign has been designed to convince the Iraqis they don't stand a chance.
At a Pentagon news conference, Col. Gary Crowder said, "I don't think the potential adversary has any idea what's coming."
Crowder, the chief of strategy at Air Combat Command, which is responsible for all Air Force warplanes, said the U.S. likely would drop 10 times as many precision-guided munitions – bombs and missiles guided by lasers and satellite signals – on the first day of conflict in Iraq as it did to open the 1991 war. He said 300-400 such weapons were dropped in 1991, suggesting that at least 3,000 would be used on the first day this time.
Still concerned Saddam may use chemical weapons, all U.S. troops are now under orders to keep their gas masks at their sides and their chem suits nearby. When the war steps off, the chem suits go on, reports CBS News Correspondent Byron Pitts, who is in the Gulf with a U.S. Marine Corps attack-helicopter unit called the Vipers.
In Baghdad, Saddam defiantly ignored the U.S. deadline to yield power.
"We are dedicated to martyrdom in defense of Iraq under your leadership," a loyal Iraqi parliament assured Saddam, and armed members of the ruling Baath party deployed behind hundreds of sandbagged defensive positions in Baghdad.
Meanwhile, the exodus from the city continued as ordinary residents fled in large numbers, hoping to find safety in the countryside.
CBS News Correspondent Lara Logan was one of the last Western reporters to leave the Iraqi capital. As she and her crew headed out of Baghdad, she says she saw surprisingly few Iraqi troops. All the fighting positions she saw were unmanned and there was little in the way of a visible military presence.
Logan said people in the city appeared increasingly nervous Wednesday; some asking reporters for confirmation the U.S. would start bombing Baghdad tonight. Most shops and businesses were closed, except for some small supply stores, and streets that were usually crowded with traffic were virtually empty.
Logan says there's almost an eerie calm on the surface, but when you talk to people you can sense the panic and fear underneath. Many people have weapons at home, some say it's to fight the Americans but others plan to hide in their houses and wait for it all to be over.
The diplomatic wheels turned still at the United Nations where foreign ministers were meeting in the Security Council at the request of the French and Germans, prominent critics of the American military operation.
"This is a sad day for the United Nations," said the organization's secretary general, Kofi Annan said. "I know that millions of people around the world share this sense of disappointment and are deeply alarmed."
Even French President Jacques Chirac conceded the obvious, saying in Paris: "The international crisis entered an acute phase yesterday that makes it probable that war in Iraq will likely break out in the coming days."