After a week of almost nightly terrorist attacks, U.S. officials have concluded that Al Qaeda is operating in Iraq along with pro-Saddam forces and is responsible for the deaths of American troops in the country, a senior coalition source said Wednesday.

The source, who spoke on condition of anonymity, confirmed similar hints from other officials, the most recent by Lt. Gen. Ricardo Sanchez (search), the commander of U.S forces in Iraq.

The source would not be drawn into estimates of how many operatives of the terrorist organization headed by Usama bin Laden were in the country, or of which specific attacks they were suspected.

At least 156 Americans have been killed in Iraq since the announced end of major combat last May.

“We have Al Qaeda in the country, yes, there’s no doubt about it,” said the source. “We also have Saddam loyalists who have nothing to lose. And we have foreign fighters who have come across the border from Syria and Iran and who see Iraq as the best place to kill Americans.”

On Tuesday, Sanchez revealed that coalition forces had captured as many as 20 suspected Al Qaeda fighters, but stopped short of confirming their affiliation with the group, which claimed responsibility for the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon. A member of the Iraqi Governing Coalition (search) made similar claims and repeated the charge that Al Qaeda has selected Iraq as its new battlefield against the U.S.

The most recent attacks in Baghdad have caused few injuries and little damage. But they have focused on the headquarters of the Coalition Provisional Authority (search), which is in the tightly controlled “green zone” of the capital. Most of the incidents have involved firing mortar rounds or rockets from crude launching devices.

Brig. General Mark Hertling, the commander of U.S. forces in the capital, said the rockets used in Tuesday’s attacks were actually launched from an old metal gutter. While acknowledging that they hit close to the CPA compound, Hertling dismissed the attacks as “militarily insignificant.” He pointed out that more Iraqis than Americans — nearly 1,000 according to some estimates — have been killed by recent terrorist incidents.

He said some 2,200 caches of weapons and ordnance have been uncovered in the Baghdad area alone, and nearly all of them are now under guard or have been destroyed. That represents progress, but is not a solution in itself.

“I had an officer say to me, ‘I get why they’re shooting at you,'” Hertling recalled. “And he said, ‘I guess I get why they’re trying to kill people from the U.N., and the Red Cross, because those people will help Iraq become free and prosperous eventually.

"What I don’t get is, why are they killing their own people, and why aren’t those people pissed off about it?”

Said Hertling, “I knew exactly what he meant. But I couldn’t answer his question.”

John Moody is senior vice president of Fox News.

John Moody is Executive Vice President, Executive Editor for Fox News. A former Vatican correspondent and Rome bureau chief for Time magazine, he is the author of four books, including "Pope John Paul II : Biography."