ISLAMABAD, Pakistan — A bomber blew himself up about a quarter-mile from President Gen. Pervez Musharraf's office Tuesday, killing seven people and deepening Pakistan's insecurity ahead of crucial elections.

Officials said the attacker detonated his explosives among police at a checkpoint in the garrison city of Rawalpindi, just south of the capital, Islamabad.

Musharraf was safely inside Army House, about a quarter-mile away, where the blast was clearly heard, said presidential spokesman Rashid Qureshi. The checkpoint guards a road leading to the president's compound and the residences of several top generals.

Police said three of their officers and four civilians were killed, along with the lone assailant. Fourteen policemen and four civilians were wounded.

"When police officers asked him to halt, the attacker panicked. And as the police tried to capture him, he blew himself up," city police chief Saud Aziz told The Associated Press. "Our officers died to protect the citizens of Pakistan."

There was no claim of responsibility, and Qureshi would not speculate on who might be to blame.

Pakistan has been rocked by a string of suicide bombings mostly blamed on Islamic extremists, including the bombing of former Prime Minister Benazir Bhutto's homecoming parade. The Oct. 18 blast killed more than 140 people in the southern port of Karachi.

Musharraf went ahead Tuesday with the scheduled opening of a highway linking Islamabad with the northwest, and warned extremists to stop killing fellow Muslims or face stern action.

"These terrorists and extremists elements must not retard the country's economic development by their senseless acts," Musharraf said, according to state-run Pakistan Radio.

The suicide attack left the area around the checkpoint strewn with human flesh and torn clothing.