KANDAHAR - Insurgents killed a total of 23 policemen across Afghanistan within 24 hours, officials said Sunday, reflecting the increasing police role in the war before the withdrawal of Nato troops.Thirteen died in roadside bomb blasts, while 10 were killed in a suicide attack.A powerful bomb killed eight police officers along with three suspected bombers they had detained on the outskirts of the troubled southern city of Kandahar, provincial spokesman Jawed Faisal told AFP."Our police had an operation in Pero Qalacha area last night. They detained several suspected insurgents," Faisal said."On the way back to the city (centre), their vehicle struck an IED (improvised explosive device). Eight police were killed and three suspects that they had detained during the operation were killed," Faisal said. Six other officers and one suspect on board a second vehicle were wounded in the blast, he said. Police spokesman Ghorzang Afridi described the bomb as "very, very powerful", saying it was an artillery shell attached to a detonator and possibly set off remotely. The officials blamed the bombing on the "armed opposition", a reference to the Taliban who have waged an insurgency against the Western-backed government since being ousted from power by a US-led invasion in late 2001.Three other policemen were killed in another roadside bombing in neighbouring Helmand on Sunday and two died in a similar attack in Farah in western Afghanistan overnight, police spokesmen said.The incidents followed a suicide bombing in the northern city of Kunduz on Saturday that killed 10 policemen including two senior officers.Afghan security forces are increasingly targeted by the Taliban as they take greater responsibility for security before the pullout of US-led Nato combat troops next year.