US-led coalition jets bombed a compound suspected of housing al-Qaida militants in eastern Afghanistan, killing seven children and several militants, while clashes in the south left dozens more suspected insurgents dead, officials said Monday. The airstrike occurred Sunday in Paktika province, hours after a suicide bomber hit a police academy bus in Kabul, killing at least 35 people, the deadliest insurgent attack in Afghanistan since the US-led invasion in 2001. The jets targeted a compound that also contained a mosque and a madrassa, or Islamic school, in the Zarghun Shah district, in an operation backed by Afghan troops. A coalition statement said "nefarious activity was occurring at the site." Spokesman Maj. Chris Belcher, a coalition spokesma, accused al-Qaida of using "the protective status of a mosque, as well as innocent civilians, to shield themselves." Early reports indicated seven children at the madrassa and "several militants" were killed, and two militants detained, the statement said. "We are saddened by the innocent lives that were lost as a result of militants' cowardice," Belcher said. Coalition troops had "surveillance on the compound all day and saw no indications there were children inside the building," Belcher said. He accused the militants of not letting the children leave the compound. "If we knew that there were children inside the building, there was no way that that airstrike would have occurred," said Sgt. 1st Class Dean Welch, another coalition spokesman. In the south, militants ambushed coalition and Afghan troops in Helmand province's Sangin district, leading to a prolonged battled involving coalition helicopters and aircraft. "Several dozen" militants were killed, a coalition statement said. Two coalition soldiers were wounded. In neighboring Kandahar province, a group of 10 militants attacked a joint coalition and Afghan patrol. The ensuing five-hour battle killed "several enemy fighters." The coalition did not give a more specific estimate of the casualties and the figures could not be independently verified due to remoteness of battle sites. The airstrikes and clashes came on the same day that a suicide bomber in the capital targeted a bus full of police trainers, killing 35 people and wounding 52 others, raising the specter in Afghanistan of an increase in Iraq-style bombings with heavy casualties. It was at least the fourth attack against a bus carrying Afghan police or army soldiers in Kabul in the last year. The blast sheared off the bus' metal sidings and roof, leaving a charred frame. Also Sunday, a roadside bomb killed three members of the US-led coalition and an Afghan interpreter in Kandahar province. The soldiers' nationalities were not released, but most troops in the coalition are American. Condemning the Kabul attack, President Hamid Karzai said the "enemies of Afghanistan" were trying to stop the development of Afghan security forces, a key component in the US-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. 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. Sunday's death toll exceeded that of a September 2002 Kabul car bombing that killed 30 people and wounded 167. 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 US, NATO, UN and Afghan officials.