Hundreds of Iraqi and U.S. troops searched fields and farms Saturday for insurgents and their hideouts in an area south of Baghdad known for attacks, and the Marines said they discovered 50 weapons and ammunition caches and a huge underground bunker west of the capital fitted out with air conditioning, a kitchen and showers.

The joint U.S.-Iraqi force operating in Latifiyah (search) to the south was backed by American air power and said it had rounded up at least 108 Iraqis, mainly Sunnis, suspected of involvement in the brutal insurgent campaign to topple the Shiite-led government.

To the west of the capital, the 2nd Marine division said its forces had discovered 50 weapons and ammunitions caches over the past four days in restive Anbar province. The military said the find included a recently used "insurgent lair" in a massive underground bunker complex that included air-conditioned living quarters and high tech military equipment, including night vision goggles.

That bunker was found cut from a rock quarry in Karmah (search), 50 miles west of Baghdad. The Marines said the facility was 170 yards wide and 275 yards long.

In its rooms were "four fully furnished living spaces, a kitchen with fresh food, two shower facilities and a working air conditioner. Other rooms within the complex were filled with weapons and ammunition," the announcement said.

The weapons included "numerous types of machine guns, ordnance, including mortars, rockets and artillery rounds, black uniforms, ski masks, compasses, log books, night vision goggles, and fully charged cell phones."

In Latifiyah, 20 miles south of Baghdad, Iraqi and American forces launched a raid as part of Operation Lightning, a week-old assault aimed at rooting out insurgents conducting raids on the capital and sapping militant strength nationwide. While Iraqi forces were in the forefront of Saturday's sweep though the semi-rural region, it was clear the U.S. military was still the driving force.

About two hours into the operation, for example, American forces voiced concern that an area covered in tall grass had not been searched. An Iraqi commander said he was reluctant to send his troops into the field for fear of an insurgent attack.

"This is a dangerous area. We need helicopters and the American army," Iraqi Brig. Gen. Najim al-Ekabi (search) said.

The American soldiers, who had spent months training Iraqi soldiers, tried to persuade al-Ekabi to send his troops, saying it was likely that weapons were hidden in the fields and alongside an irrigation canal.

Army Capt. Jason Blindauer of the 2nd Brigade, 10th Mountain Division told al-Ekabi the force had orders to search the area. "No one is going to do it better than your group," Blindauer said.

Al-Ekabi asked for a private meeting with the Americans and departed shortly afterward in a large convoy, ostensibly to conduct the search.

Maj. Ronny Echelberger (search) later went into the area with American forces and searched a few homes, saying was not been sure the Iraqi search had been sufficiently thorough.

The Iraqi army's reliance on U.S. troops was evident in other ways. Echelberger had to show an Iraqi brigade commander his location on a map shortly before Iraqi troops launched the operation, and a few minutes later Iraqi soldiers fired hundreds of rounds when they mistakenly thought they saw an insurgent.

"These guys are doing baptism by fire. It takes time," Blindauer said.

Operation Lightning is being watched closely as a bellwether of when Iraqis can take control of their own security, a key to the U.S. exit strategy more than two years after Saddam Hussein's ouster.

Interior Minister Bayan Jabr has said at least 700 suspected insurgents have been rounded up in the sweep, which has also killed at least 28 militants. U.S. Lt. Col. Michael Infanti said at least 221 people had been detained since last Wednesday by forces carrying out a sweep of Baghdad's southern districts. It was unclear if that number was in addition to the 700 given by Jabr.

Also Saturday, a suicide car bomber blew himself up at an Iraqi police checkpoint on a main road connecting northern Mosul with the nearby city of Tal Afar, killing two officers and wounding four. Four others were hurt in a roadside bombing as they went to help their fallen colleagues, Mosul police Lt. Zaid Ahmed Shakir said (search).

An Iraqi believed to be a terror leader in the north was captured by U.S. and Iraqi forces in Mosul, 225 miles north of Baghdad. He was identified as Mullah Mahdi and was caught along with his brother, three other Iraqis and a non-Iraqi Arab, Iraqi army Maj. Gen. Khalil Ahmed al-Obeidi said.

Mahdi was affiliated with the Ansar al-Sunnah Army, one of Iraq's most feared terror groups, and had links to the Syrian intelligence service, al-Obeidi said without elaborating. Iraqi and U.S. officials have accused Syria of facilitating the insurgency by allowing foreign fighters to cross its borders, but Damascus denies the allegation.

Mahdi was wanted in connection with car bombs, assassinations "beheadings of Iraqi policemen and soldiers and for launching attacks against multinational forces," in Mosul, al-Obeidi said.

In addition, 19 suspected insurgents — including a Jordanian and a Syrian — were arrested in raids in Baghdad's western Abu Ghraib district, Iraqi Lt. Col. Abu Fahad Alkhasali said.