KABUL, Afghanistan (AP) – Seven children were killed in an American-led coalition airstrike targeting suspected Al Qaeda militants in eastern Afghanistan, a coalition statement said Monday. The strike came hours after the deadliest insurgent attack since the Taliban fell in 2001.

A suicide bomber on Sunday destroyed a bus full of police instructors at Kabul’s busiest transportation hub, killing 35 people and wounding 52, officials said.

The airstrike, which had the support of Afghan troops, was launched on a compound that also contained a mosque and a madrassa, or Islamic school, in the Zarghun Shah district of Paktika province.

Early reports said seven children at the school were killed in the strike and that “several militants” also were killed, the coalition statement said. Two suspected militants also were detained.

Coalition troops had “surveillance on the compound all day and saw no indications there were children inside the building,” said Major Chris Belcher, a coalition spokesman. He accused the militants of not letting the children leave the compound that was targeted.

“If we knew that there were children inside the building, there was no way that that airstrike would have occurred,” said Sergeant 1st Class Dean Welch, another coalition spokesman.

Afghan officials have recently said that civilian deaths are the main concern of Afghans, and President Karzai has repeatedly called for foreign troops to do more to prevent civilian casualties.

Sunday’s enormous blast, which raised the specter of an increase in Iraq-style bombings with heavy casualties, was at least the fourth attack against a bus carrying Afghan police or army soldiers in Kabul in the last year. The bomb sheared off the bus’ metal sidings and roof, leaving a charred frame.

“Never in my life have I heard such a sound,” said Ali Jawad, a 48-year-old who was selling phone cards nearby. “A big fireball followed. I saw blood and a decapitated man thrown out of the bus.”

The explosion was the fifth suicide attack in Afghanistan in three days, part of a sharp spike in violence around the country.

In the south, in Kandahar province, a roadside bomb killed three members of the American-led coalition and an Afghan interpreter. The soldiers’ nationalities were not released, but most in the coalition are American.

Condemning the Kabul attack, Mr. Karzai said the “enemies of Afghanistan” were trying to stop the development of Afghan security forces, a key component in the American-NATO strategy of handing over security responsibilities to the Afghan government one day, allowing Western forces to leave.

A self-described Taliban spokesman, Qari Yousef Ahmadi, said a Taliban suicide bomber named Mullah Asim Abdul Rahman caused the blast. Ahmadi called an Associated Press reporter from an undisclosed location. His claim could not be verified.

Zemeri Bashary, the spokesman for the Interior Ministry, said late Sunday that 35 were killed and 52 wounded in the blast. Karzai’s office said 22 police instructors died, indicating that 13 of the dead were civilians.

At least one person survived the 8:10 a.m. bus blast. Nasir Ahmad, 22, a janitor at the police training academy, was sitting in the back of the bus when the bomb exploded. Speaking from a hospital bed where he was recovering from wounds to his face and hands, he said: “There were between 30 to 40 police instructors in the bus.”

It was the only full sentence he managed to utter before stopping from exhaustion.

At the entrance to the hospital, a blue plastic trash can overflowed with the bloodied shoes and sandals of victims.

Interior Minister Zarar Ahmad Muqbal said initial indications were that a suicide bomber boarded the bus as it stopped to pick up police instructors at an open-air bus station in central Kabul. Such a suicide attack would represent a sizable jump in lethality compared to more typical Taliban suicide bombings, which often kill far fewer people.

Major John Thomas, a spokesman for NATO’s International Security Assistance Force, said it was too early to tell if the attack was a sign of more lethal bombings to come, or heavier involvement by al-Qaida. NATO commanders have long predicted a rise in suicide attacks this year.

A civilian bus was driving just in front of the police vehicle and was damaged when the bomb went off. A police officer at the scene said the civilian bus’ position likely prevented more civilian casualties.

Afghan government officials, police and army soldiers are commonly targeted by insurgents trying to bring down Karzai’s American-backed government, and buses carrying Afghan police and army soldiers are common targets.

In May, a remote-control bomb hit an Afghan army bus in Kabul, killing the driver and wounding 29 people. In October, a bomb on a bicycle exploded as a police bus went by in Kabul, wounding 11. Last July, a remote-controlled bomb blew up near an Afghan army bus in downtown Kabul, wounding 39 people on board.

Insurgency-related violence has killed more than 2,400 people in Afghanistan this year, mostly insurgents, according to an AP count based on figures from American, NATO, U.N. and Afghan officials.

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Associated Press reporters Noor Khan in Kandahar and Rahim Faiez and Amir Shah in Kabul contributed to this report.