A lieutenant of Iraq's most feared terrorist leader Abu Musab al-Zarqawi (search) was captured a few days ago in Mosul, and Iraqi troops searching suspected terrorist hideouts in Fallujah (search) discovered a laboratory with manuals on manufacturing explosives and toxins — including anthrax, Iraq's national security adviser said Thursday.

Also, the U.S. military said it discovered the "largest weapons cache to date in the city of Fallujah." The weapons — including anti-tank mines and a mobile bomb-making lab — were found inside a mosque used by an insurgent leader. Troops also found documents detailing hostage interrogations, the military said.

Five Arab foreign fighters who escaped from Fallujah were arrested near southern Basra, where they were planning to attack coalition bases and police stations, authorities said.

National security adviser Qassem Dawoud identified al-Zarqawi's alleged lieutenant as Abu Saeed, but he gave no further details.

Insurgents rose up this month in Mosul, Iraq's third-largest city, in support of rebels in Fallujah, who were routed by U.S. and Iraqi forces in an offensive that began Nov. 8. U.S. and Iraqi authorities managed to regain control of Mosul after the entire 5,000-member police force disintegrated.

Al-Zarqawi, whose Al Qaeda (search)-linked group has been responsible for numerous car bombings and beheadings of foreign hostages, including three Americans and a Briton, was believed headquartered in Fallujah. But the Jordanian-born extremist managed to escape the siege.

The United States has offered a $25 million reward for al-Zarqawi's capture — the same amount being offered for Usama bin Laden and his deputy, Ayman al-Zawahri.

In Fallujah, Iraqi forces uncovered a lab in the southwestern district of the city, where pockets of insurgents are still holding out following the assault.

"We also found in the laboratory manuals and instructions spelling out procedures for making explosives," Dawoud said. "They also spoke about making anthrax."

Dawoud showed pictures of a shelf containing what he said were various chemicals.

Earlier, the U.S. military said it had uncovered the largest arms cache yet inside the mosque of an insurgent leader in Fallujah. Troops found small arms, artillery shells, heavy machine guns, and anti-tank mines Wednesday inside the Saad Abi Bin Waqas Mosque in central Fallujah where Sunni rebel leader and imam Abdullah al-Janabi often spoke, the U.S. military said in a statement.

U.S. Marine officers say they so far have found enough weapons in Fallujah to refuel a nationwide rebellion.

Elsewhere in the mosque compound, troops also found what may be a mobile bomb-making factory housed in a truck, as well as mortar systems, rocket-propelled grenades, launchers, recoilless rifles and parts of surface-to-air weapons systems, the statement said.

The troops also found "documents that detailed insurgent interrogations of recent kidnap victims," the statement said.

U.S. and Iraqi troops continue to sweep the city amid sporadic gun battles with rebel holdouts.

Five Arab foreign fighters who escaped from Fallujah were arrested near southern Basra, where they were planning to attack coalition bases and police stations, authorities said.

Basra Police Chief Brig. Mohammed Khazim said the men were stopped late Wednesday at a checkpoint in Qurnah, about 37 miles north of Basra, and "personal weapons" were found in their four-wheel-drive vehicle. The men said they came from Fallujah.

Defense Minister Hazem Shaalan said earlier this week that about 60 Arab fighters have been arrested during the Fallujah assault. The U.S. and Iraqi leadership have repeatedly maintained that foreign fighters from neighboring Arabic countries have joined the insurgency.

Two of the captured fighters were identified as being from Saudi Arabia, two from Tunisia and one from Libya.

The men left Fallujah four days ago, traveling to Baghdad for a couple days during which they worked with another group to carry out attacks in the capital. They did not say what kind of attacks. They said they then headed to Basra with plans to attack police stations and coalition bases in the area. The bulk of Britain's 8,500 troops in Iraq are based around the southern port city of Basra.

The men said they were supposed to be assisted by another group that had already infiltrated Basra, Khazim said. They were told that the weapons needed to carry out the attacks already were hidden inside the city, he said.

In Baghdad, the U.S. Embassy said Thursday that an American civilian working with the embassy was killed during an attack outside the Green Zone. In Washington, Secretary of State Colin Powell identified the man as James Mollen, a State Department education specialist who served as a consultant to Iraq's minister of education and the minister of higher education.

Spokesman Pete Mitchell said Mollen was traveling in a vehicle outside the protected Green Zone, which houses the U.S. and Iraqi leadership, when he came under gunfire Wednesday afternoon.

Meanwhile, an explosion hit a domestic pipeline Thursday that runs from northern Kirkuk to the Beiji refinery, oil officials said.

The early morning sabotage took place in the Fatha area, about 70 miles southwest of Kirkuk, said a source with the state-owned Northern Oil Co. It was unclear what impact the attack will have on domestic production. Repairs will take about five days, the official said.

Saboteurs also attacked two oil wells near the Himreen Mountains, 75 miles south of Kirkuk, but the oil continued flowing, the official said.