US bombers and jet fighters unleashed 40,000 pounds of explosives during a 10-minute air strike in Iraq Thursday, flattening what the military called al-Qaida safe havens on the southern outskirts of the capital. The massive attack, carried out above approaching US and Iraqi troops, was part of Operation Phantom Phoenix, a nationwide campaign launched Tuesday against al-Qaida in Iraq. The air raid was followed by a ground attack that led to 12 arrests and the discovery of two houses used to torture kidnap victims, according to an Iraqi army officer. He said the troops faced no resistance. A military statement said two B-1 bombers and four F-16 fighters dropped the bombs on 40 targets in Arab Jabour in 10 strikes. Al-Qaida fighters are believed to control Arab Jabour, a Sunni district lined with citrus groves and scarred by daily violence. "Thirty-eight bombs were dropped within the first 10 minutes, with a total tonnage of 40,000 pounds," the statement said. The Iraqi army officer, whose unit is in the Arab Jabour area, said the air strikes began at 8 a.m. and led to the burning of several citrus groves and the destruction of two houses used by gunmen. He said soldiers confiscated documents and weapons including AK-47s. The army officer spoke on condition of anonymity because he was not authorized to speak to the media. But Sheik Mahmoud Kamil Shebib, a local Sunni leader who has turned against al-Qaida in Iraq, independently gave a similar account. Moahmoud Chiad, who lives on the edge of Arab Jabour, said that when he left his house in the morning, he was surprised to see many US-Iraqi checkpoints in the area with Iraqi security forces ordering people, through loudspeakers, to stay home. "After this, we saw US helicopters hovering over the area while the sounds of jet fighters were also heard," he said. "Minutes later, there was the sounds of big explosions. We saw fire and smoke coming out from some groves. Then, the gunfire crackled in the groves, but it ended by noon." The attack came a day after the US military reported that nine American soldiers were killed north of the capital in the first two days of a new offensive. Many militants have fled US and Iraqi forces massing north of Baghdad in Diyala province. Like Arab Jabour, Diyala is an agricultural area of palm and citrus groves that has defied the trend toward lower violence. The campaign's scope is nationwide but is mainly focused on gaining control of Diyala and its most important city, Baqouba, which al-Qaida has declared the capital of its self-styled Islamic caliphate. Six soldiers were killed and four were wounded Wednesday in a booby-trapped house in Diyala, the US command said. It also announced that three US soldiers were killed and two wounded in an attack Tuesday in Salahuddin province, north of Diyala. Al-Qaida fighters retreated north from Diyala, presumably to Salahuddin, the top US commander in northern Iraq, Maj. Gen. Mark P. Hertling, told reporters in Baghdad on Wednesday. "Operational security in Iraq is a problem," he said, noting that the Iraqi army uses unsecured cell phones and radios. "I'm sure there is active leaking of communication." Hertling said his troops had killed 20 to 30 insurgents in the first two days of the operation. It was unknown how many were killed in Thursday's strike. In central Baghdad early Thursday, two bombs exploded nearly simultaneously close to a military checkpoint, killing two policemen and one soldier, police said. Eleven others were wounded in the attack, including four civilians.