A bomber blew himself up less than half a kilometer (about a quarter-mile) from President Gen. Pervez Musharraf's office, killing seven people and deepening Pakistan's insecurity ahead of crucial elections. Officials said the attacker detonated his explosives among police Tuesday at a checkpoint in Rawalpindi city, just south of the capital, Islamabad. Musharraf was safely inside Army House - but the blast was clearly heard there - about a half-kilometer (quarter-mile) away, said presidential spokesman Rashid Qureshi. No one claimed responsibility. Qureshi would not speculate on who might be to blame.