Around two dozen Taliban armed with rocket launchers and automatic weapons attacked a police checkpost in northwest Pakistan Sunday, killing three policemen and wounding another, police said. The militants struck before dawn in Shangla, a district of troubled Khyber Pakhtunkhwa province near Swat where the army claimed to have flushed out Taliban rebels after a fierce offensive in early 2009. \"Three policemen were killed and one injured in the attack,\" district police chief Jahanzeb Khan told AFP by telephone. Shah Hussain, another senior police officer, said Taliban militants were involved in the attack. \"Taliban came from the nearby mountains and managed to flee after the attack,\" he said. Nearly 4,500 people have been killed across Pakistan in attacks blamed on Taliban and other Islamist extremist networks based in the border tribal belt since government troops stormed a radical mosque in Islamabad in 2007. Militants have stepped up their activities, mostly targeting security forces, to avenge the death of Osama bin Laden who was killed in a covert operation by US Navy SEALs in the Pakistani garrison city of Abbottabad in May.