About 80 foreign fighters who were captured in the northeast region of Iraq within the past 24 hours were in the U.S.-led coalition's custody Thursday and being interrogated about why they were in Iraq, senior defense officials told Fox News.

The fighters were nabbed between the city of Mosul (search) and the Syrian border. The operation, only a day old and set to conclude shortly, was conducted by elements of the 101st Airborne Division (search) and the 3rd Armored Cavalry Regiment (search).

Officials said the foreign fighters come from countries such as Saudi Arabia, Yemen, Sudan and Syria. They were found with nearly 1 million Iraqi Dinars, and some $75,000 in U.S. currency. Initial reports indicate they were relatively lightly armed — mostly with machine guns, shot guns and sniper rifles.

In other developments, a U.S. military convoy was ambushed near Khaladia (search), about 21 miles west of Fallujah (search), on Thursday.

A U.S. personnel carrier and another vehicle were struck by the rocket-propelled grenades. One soldier was wounded.

Fallujah is in the so-called "Sunni triangle" (search) of Iraq, where most of the attacks against coalition forces have taken place.

A senior administration official told Fox News that U.S. intelligence is still trying to put together who these foreign fighters are and who is recruiting them.

But the official said the numbers range from "at least 1,000 to as high as 3,000."

The official did say flatly that "recruiting is going on to bring jihadists to Iraq." But the official said there is no clear information on who is doing the recruiting — whether it is regime supporters in Iraq, or whether it is Al Qaeda elements or those linked with them.

State Department spokesman Richard Boucher said Thursday that U.S. officials have had "recent" talks with Syria about clamping down on its borders. It's well known that many foreign fighters have entered Iraq through that country.

"As of, what, two weeks ago, when we were talking about this we were making the point, repeatedly, to the Syrians," Boucher said.

"We have made clear all along that the presence of foreign fighters in Iraq was dangerous, that the ability of people to get across borders, whether with or without the consent of government, was one of the problems and a problem that we wanted to deal with."

To counter this problem, Boucher noted that U.S.-led forces are helping to rebuild the Iraqi border patrol and boost police forces. The coalition is also working diplomatically with neighboring countries to track down terrorists and discourage them from going to Iraq, Boucher said.

U.S. and coalition forces intend to continue patrols in this wide area of western Iraq, hoping for more successes.

"This is a great break in news," said Fox News military analyst, Ret. Lt. Col Bill Cowan. "I'm speculating this is probably a result of good information from the Iraqi people who don't want these people in their neighborhood."

Lt. Gen. Ricardo Sanchez, the top American military commander in Iraq, said Thursday the country was becoming the key battlefield for the U.S.-led war on terrorism — a war he said would not end quickly.

"It's clear to me that this is the next battleground in the global war on terrorism that we have been on now for two years," Sanchez told reporters.The war in Iraq was "a natural follow-up battle in that war on terrorism" that began with the U.S.-led ouster of the Taliban regime and its Al Qaeda allies from Afghanistan.

Sanchez acknowledge the threat from imported terrorism.

"There is a threat, a terrorist threat here in this country. There are people that are infiltrating into the country to attack the coalition and American forces. So that would not be unexpected," he said.

American officials have repeatedly said terrorist foreign fighters were infiltrating the country but have not produced any captives to support the allegations. Five bombings — two of them thought to be the work of suicide attackers — in as many weeks carry some of the hallmarks of terrorism.

In a Thursday raid in Tikrit, troops from the 4th Infantry's 1st Battalion, 22nd Infantry Regiment, shut down two bomb-making factories and detained five Iraqis. The raid was one of seven in northeastern Iraq in which U.S. troops detained 48 people and confiscated more than 30 AK-47 rifles, dynamite and plastic explosives, nine mortar rounds and other weapons and ammunition.

The Qatar-based Arab satellite broadcaster Al-Jazeera reported Thursday that one of its correspondents, taken into custody by American forces in Baghdad the day before, had been released. The U.S. military said Atwar Bahjat was arrested for having broken unspecified "ground rules."

Military sources told Fox News that two Al-Jazeera staffers were being held in Baghdad Thursday by U.S. forces in connection with the investigation of the death of a U.S. serviceman in Baghdad Wednesday.

A U.S. military bomb disposal technician was killed when a roadside improvised explosive device he was trying to disarm exploded. Sources told Fox News that there are indications the Al-Jazeera crew may have been tipped by someone to an upcoming incident, and was on the scene as the bomb exploded.

Also Thursday, an American soldier died and two others were slightly injured when a tire they were changing on a "heavy expanded mobility tactical truck" exploded, the U.S. Central Command said. The accident occurred near Balad, 45 miles north of Baghdad.

Fox News' Jim Angle, Bret Baier, Ian McCaleb, Greg Palkot, Teri Schultz and Dan Springer and The Associated Press contributed to this report.