ARLINGTON, Va. — After "a careful, measured beginning" to the campaign against Saddam Hussein, a massive air campaign that opened Friday marked the beginning of the full-scale, all-out war against the regime, senior military leaders said.

"Operation Iraqi Freedom is fully under way," Defense Secretary Donald Rumsfeld told reporters in a standing-room-only press briefing at the Pentagon, just moments after a wave of hundreds of airstrikes sent clouds of fire and smoke billowing over Baghdad.

"The air campaign began in earnest at 1 p.m." Eastern Standard Time, Rumsfeld said.

Air Force Gen. Richard Myers, Chairman of the Joint Chiefs of Staff, who joined Rumsfeld in the briefing, promised that the initial wave of strikes were just the start of the day's air campaign.

"Several hundred military targets will be hit in the next several hours," Myers said.

Meanwhile, the ground campaign, which began Thursday about 10 p.m. EST with the 3rd Infantry Division rolling into southern Iraq, proceeded to the point where U.S. and British forces penetrated "close to 100 miles inside" the country, Myers said.

"Clearly we're moving towards our objective," Myers said, "but we must not get too comfortable ... there are still a lot of unknowns out there."

Even before the U.S. military began to bring its full might to bear in Iraq, the government of Saddam Hussein was already starting to crumble, Rumsfeld said.

"The Iraq regime is starting to lose control of their country," he said. "Confusion of Iraqi officials is growing. ... Their ability to control [their military defenses] is slipping."

Intelligence reports indicate that the ability of the Iraqi leadership to communicate with one another and Iraqi military commanders has deteriorated as a result of "early battlefield preparations — "airstrikes that began Wednesday against various government and military installations, Rumsfeld said.

But there is still no solid evidence to show that the very first action of the war, a "target of opportunity strike" Wednesday against a southeast Baghdad residence where Saddam and his senior officers was thought to be hiding, harmed or killed the dictator himself, Rumsfeld said.

"There's no question that the strike on the leadership headquarters was successful," Rumsfeld said. "The question is, 'Who was in there?'"

Asked whether Saddam is still in charge of Iraq, Rumsfeld replied, "I don't know."

"Until there's solid evidence [the regime] doesn't exist, we have to assume that it's in place and functioning," he said.

Rumsfeld and Myers also expressed regret over the deaths of four Marines and eight of Britain's Royal Marines killed in the CH-46 helicopter that crashed Friday in Kuwait.

U.S. Central Command officials also have confirmed that two U.S. Marines with the 1st Marine Expeditionary Force also have been killed — one in a gunfight as his unit advanced on an oil field, the other while fighting enemy Iraqi forces near the port of Umm Qasr.

"Our hearts go out to their families," Rumsfeld said.

"These brave men died fighting for their nation and for freedom," Myers added.

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