A suicide attacker set off a bomb less than half a quarter-mile from the military headquarters where President Gen. Pervez Musharraf was staying Tuesday, killing seven people, police said.
The blast will likely feed fears for the country's stability, just as it prepares for crucial parliamentary elections and faces a growing threat from Islamic militants.
There was no claim of responsibility. Musharraf's spokesman Rashid Qureshi declined to speculate on who was to blame.
However, he said it followed a string of bloody suicide attacks including the bombing of former Prime Minister Benazir Bhutto's homecoming parade. The Oct. 18 blast killed more than 140 people in Pakistan's largest city, Karachi.
Qureshi said that extremists were abusing Islam to justify atrocities and that Musharraf, a key ally in the U.S.-led war on terrorism, would not be swayed.
"He's said time and again that the only threat facing Pakistan is from extremism and terrorism, and there's no way he's going to change his attitude toward these people," Qureshi said.
Police said three of their officers and four civilians were killed along with the lone assailant. Fourteen policemen and four civilians were wounded, he said.
"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."
Women and children among dead
The attack left the area around the checkpoint strewn with human flesh and torn clothing. The checkpoint guards a road leading to Army House and the residences of several top generals.
An AP photographer saw emergency workers remove the body of an elderly man, killed as he was riding by on a bicycle.
Police said women and children aboard a passing minibus were also among the dead and wounded. Television footage showed schoolbags abandoned on the seats of the vehicle, its windows blown out.
Investigators cordoned off the area to retrieve evidence. A policeman climbed an overhanging tree to dislodge part of the bomber's severed head.
Fortified army posts at the checkpoint and the nearby gate to the residence of Gen. Tariq Majid, the army's No. 3 commander, were scarred with shrapnel and spattered with blood.
Pakistan has been rocked by a string of suicide bombings, including two blasts that killed 25 people in Rawalpindi, a garrison city just south of Islamabad, on Sept. 4.
The violence has surged since Musharraf's decision in July to crack down on militants near the Afghan frontier.
Pakistan acknowledges that the area has become a haven for Taliban militants fighting in Afghanistan, while the U.S. worries that al-Qaida may be using it to plot new attacks on the West.
3 attempts on Musharraf's life
Last week, Pakistan sent troops to tackle supporters of a pro-Taliban cleric in the northwestern district of Swat. Officials say four days of violence in the scenic, once-peaceful mountain region has killed about 100 people.
Musharraf, who has survived at least three attempts on his life, is widely expected to join forces with Bhutto in a U.S.-friendly alliance, if her party fares well in January parliamentary elections.
Both are stressing the need for moderates to pool their strength to defeat extremism and terrorism — making them prime targets for Islamic hard-liners who deride them as U.S. stooges.
Bhutto's Pakistan People's Party said Tuesday's attack showed that the current military-led administration was failing to roll back extremism.
"A democratic government is better equipped to take up such a battle and fight it to the finish because its policies will be backed by the masses," said party spokeswoman Sherry Rehman.
Sheikh Rashid, a senior Cabinet minister, said extremists were trying hard to secure a "big catch."
"There may be some forces who want to give some big message that they are here, they are in Rawalpindi, they are in Islamabad," Rashid told Dawn News television. "This is a very critical time and critical situation."