Baghdad ? U.S. and Iraqi troops moved against al-Qaida 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 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 strongholds in the western and eastern parts of Mosul, Iraq’s third largest city, where insurgents are believed 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, complained that the sweep was “unorganized” and that public warnings of the coming raids enabled al-Qaida fighters to flee, as they have done ahead of previous 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.

American Marines were operating farther south, near Lake Tharthar, a remote desert region that has been a refuge for al-Qaida 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, told 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 material 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 believe 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 fighters hid in the desolate region after losing control of those cities, and the U.S. military believes the group has been using it for training and as a supply route.

Al-Qaida in Iraq has been weakened by the U.S. troop buildup over the past year but appears far from defeated.

In an attack that bore the group’s hallmarks, a suicide bomber Wednesday blew himself up in a funeral tent in a village west of Baghdad, attended by many local U.S.-backed Sunni tribesmen fighting al-Qaida militants. The attack killed 22 people and wounded 40, according to police Col. Faisal al-Zubaie. The U.S. military on Thursday put the death toll at 14; there was no immediate explanation for the discrepancy.