BAGHDAD - U.S. and Iraqi troops moved against al-Qaida in Iraq on two separate fronts Thursday, with house-to-house searches in Mosul and an operation in the desert to stanch the flow of insurgents and weapons to that northern city.

With the new sweep, Prime Minister Nouri al-Maliki is aiming to put down Sunni extremists after launching two other major offensives elsewhere in as many months targeting Shiite militants. Mosul, a key transport crossroads between Baghdad, Syria and other points, is considered the last major urban base of al-Qaida in Iraq after the group lost strongholds in western Anbar province.

U.S.-backed Iraqi troops searched homes, and the U.S. military announced that the forces in Mosul captured a suspected al-Qaida in Iraq figure involved in organizing car bombings and smuggling foreign fighters into the country.

There were no reported clashes during the searches in known al-Qaida in Iraq strongholds in the western and eastern parts of Mosul, Iraq's third-largest city, where insurgents are thought to use the cover of sheep and produce markets to smuggle cash, weapons and foreign fighters from nearby Syria.

Sheik Fawaz Jarba, a leader of Sunni tribes in Mosul opposed to al-Qaida in Iraq, complained that the sweep was "unorganized" and that public warnings of the coming raids enabled al-Qaida in Iraq fighters to flee, as they have done ahead of campaigns elsewhere.

"Al-Qaida has gone into hiding and have gone elsewhere," Jarba said, adding that his tribal fighters were prepared to join the crackdown but that al-Maliki had not asked them to.

Marines were operating farther south, near Lake Tharthar, a remote desert region that has been a refuge for al-Qaida in Iraq fighters and a back channel for supplying the network in the north.

"We're trying to shut down the rat lines," Marine Brig. Gen. Richard Mills, who is heading up the operation, said during a briefing at a mobile command post set up in the Mameluke desert.

U.S. Marines on Thursday searched an abandoned mud house, uncovering six weapons caches, including components for building roadside bombs.

Marine Capt. Josh Biggers said they discovered evidence that insurgents had recently used the area: broken egg shells scattered across a floor in one room, new electrical fixtures and the outline on the floor of what troops think may have been a generator.

"Somebody was definitely here," said Biggers, 30, of Edmond, Okla.

Lake Tharthar -- once Saddam Hussein's favorite fishing spot -- lies between Mosul and the former Sunni insurgent strongholds of Fallujah and Ramadi. Many al-Qaida in Iraq fighters hid in the desolate region after losing control of those cities, and the U.S. military thinks the group has been using it for training and as a supply route.

IRANIANS INJURED: Gunmen opened fire on a car carrying three Iranian Embassy employees in Baghdad on Thursday, wounding them and their Iraqi driver, an embassy spokesman said.

Iraqi police confirmed the attack, according to a Washington Post report, but did not provide further details or say who they thought could be behind it. Iran's official IRNA news agency blamed U.S. forces.

A U.S. military spokesman, Maj. Brad Leighton, dismissed the allegation. "We're not in the business of assassination," he said.

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