A suicide bomber riding a motorcycle blew himself up alongside a government bus on a busy road in Rawalpindi on Thursday afternoon, the latest in a spate of attacks following the Pakistani army's military offensive against the Taliban. The initial reports of the death toll from the blast, which occurred about 4:15 p.m. along a main road in the city that houses the Pakistani military headquarters, ranged from one to six people killed, with as many as 30 people injured, according to police. The senior police official in Rawalpindi, Nasir Durrani, told reporters that the bomber struck along the gas-tank side of a white bus carrying about 25 people. The bus was coming from a government facility that is used for Pakistan's nuclear program, government officials said, and the blast struck within a couple miles of military headquarters. 'We have been receiving threats to government installations for a while,' Durrani said. President Asif Ali Zardari and other top officials condemned the attack and called for an investigation into the incident. For the past two months Pakistan has intensified military operations against Taliban fighters, using thousands of ground troops and aircraft bombing runs. Taliban commanders have vowed to target government-related facilities in response to the military operations and the ongoing American drone attacks. Suicide bombings, once relatively rare in Pakistan, have become an increasingly common weapon for insurgents. Special correspondent Shaiq Hussain contributed to this report. 