Pakistan’s second city of Lahore erupted in chaotic gunfire this morning following a suspected suicide bomb attack. At least 22 people were killed in what the government said is revenge for its offensive against the Taliban in the northern Swat Valley.The target of the bombing was a police headquarters. Just before the blast a group of up to five men got out of a car and opened fire on guards at the gate. The attackers failed to gsmash their way into the police compound but their vehicle packed with explosives exploded, severely damaging an ambulance service building and devastating the office of the military intelligence agency. It is the fifth attack since fighting in the Swat region intensified late last month. Rescuers worked all day in the rubble in the hope of finding survivors. But with nearly 300 people wounded it is feared the number of dead could rise. Several suspects have been arrested but no group has yet claimed to have launched the attack. Lahore was hit two months ago when suspected Taliban fighters stormed the city’s police training academy and killed eight recruits in a siege that lasted hours.