US warplanes dropped 40,000 pounds of bombs on Thursday in a sudden and massive strike on more than 40 al- Qaeda targets clustered in date palm groves on Baghdad’s southern outskirts, the military said.

The US Air Force sent two B-1 bombers and four F-16 fighter jets, aiming at three large target areas in Arab Jabour, a lush area just south of the capital that has become a haven for fighters driven out of other areas.

The attack formed part of Operation Phantom Phoenix, a countrywide offensive against al Qaeda guerrillas that US forces announced this week. It followed the death of six American soldiers on Wednesday by an explosion in a booby-trapped house in northern Diyala province. Three other soldiers were killed on Tuesday in Salahuddin province. “Thirty-eight bombs were dropped within the first 10 minutes, with a total tonnage of 40,000 pounds,” the military said in a statement. “Each bomber passed over twice and the F-16s followed to complete the set.” A spokeswoman for US forces in central Iraq, Major Allayne Conway, said it was too soon to say how many people had been killed in the airstrikes, but a damage assessment was underway.