An enormous bomb ripped through a police academy bus in a crowded area of Kabul on Sunday, killing more than 35 people and wounding 35 others in the deadliest insurgent attack in Afghanistan since the US-led invasion in 2001. The Taliban claimed responsibility. The thunderous explosion - which sheared the metal sidings and roof off the bus, leaving only a charred skeleton - represented a massive leap in scale from previous Taliban or al-Qaida bombings here, raising the specter of an increase in Iraq-style attacks in Afghanistan. At least 35 people were killed, including 22 policeman, said Ahmed Zia Aftali, the head of Kabul's military hospital. A purported Taliban spokesman, Qari Yousef Ahmadi, said a Taliban suicide bomber named Mullah Asim Abdul Rahman caused the blast. Rahman, 23, was from Kabul province, said Ahmadi, who called an Associated Press reporter by satellite phone from an undisclosed location. His claim could not be verified. Unidentifiable body parts littered the blast site as far as 30 meters from the bus. Hundreds of police and investigators inspected the scene, while some pulled bodies from the wreckage shortly after the blast. The bus was carrying police recruits when the bomb went off inside it around 8:10 a.m. local time, said Zalmai Khan, the deputy police chief of Kabul province. Despite the Taliban claim, officials were trying to determine if the explosion, which went off in the front of the bus, was caused by a suicide attacker or a bomb that had been planted. Wali Mohammad, an eyewitness who was driving his car just behind the bus, said he "saw a big fire and dust in front of me." "There were a lot killed and wounded, both police and civilians," he said. The blast happened at a crowded bus station used by both police and civilians near the Kabul governor's house. A civilian bus driving close to the police bus also was damaged. Afghan government officials, police and army soldiers are commonly targeted by insurgents trying to bring down the US-backed government of President Hamid Karzai. A police and army force that can provide security around the country on its own is essential to the US and NATO strategy of one day handing over security responsibilities to the Afghan government, allowing Western forces to leave. Buses carrying Afghan police and army soldiers have been targeted before. In May, a remote-control bomb hit an Afghan army bus in Kabul, killing the driver and wounding 29 people, including 22 soldiers. In October, a bomb placed 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. At least 307 Afghan security officials have been killed in violence so far this year through June 15, according to an AP tally of figures from the US, UN, NATO and Afghan authorities. Sunday's attack is the deadliest by insurgents since the fall of the Taliban. Last September, a suicide bomb attack left 16 dead, including two American soldiers close to the US embassy in the capital. Days later, a suicide attack near the Interior Ministry, which is in charge of police, left 12 people dead and over 40 others wounded.