In Pakistan, at least 21 soldiers were killed and several others wounded when a suicide bomber disguised as a schoolboy today blew him up at the parade ground of a heavily guarded army centre in the northwest.The bomber struck when soldiers were on parade at the ground inside the Punjab Regimental Centre within the cantonment in Mardan city, 60 km northeast of Peshawar.The powerful explosion was heard from several kilometres away. The injured were taken to a nearby military hospital, where an emergency was declared. Officials said several of the injured were in a serious condition.Witnesses were quoted by TV news channels as saying that the young bomber was wearing a school uniform. A school run by the army is located near the parade ground. No group claimed responsibility for the attack.