The blast Sunday was one of Islamabad's deadliest in recent memory, killing at least 18 people and wounding dozens. Mourners held funeral prayers for the slain Monday, while Interior Ministry chief Rehman Malik said investigators found a severed head, possibly the attacker's.
Monday evening, six small explosions struck the southern city of Karachi, wounding at least 37 people and intensifying unease in Pakistan. Babar Khattak, Sindh province police chief, said five men had been detained but gave no details on their identities or a motive for that attack.
Speculation linked the Islamabad blast to the first anniversary of the army's crackdown on Islamic militants at the Red Mosque. A conference at the mosque drew thousands Sunday, and a mosque official condemned the bombing, one of many aimed at security forces in Pakistan.
Political leaders, too, decried the blast. Prime Minister Yousuf Raza Gilani said it was "against humanity," while President Pervez Musharraf, whose alliance with the U.S. in the war against extremists has fueled resentment among his countrymen, urged resilience.
Asif Ali Zardari, head of the main ruling party, insisted the attack "would only strengthen the resolve of the government to confront the militants and extremists head on." But the attack also promised to raise more concerns about government moves to negotiate with militants.
The U.S. Embassy advised American citizens not to go to the Red Mosque neighborhood for fear of more violence.
Pakistani officials were still trying to determine the identity of the bomber.
Hours after the blast, the Interior Ministry chief told Geo TV the suspect was a teenage boy. "All witnesses say that a 15- or 16-year-old boy, who had a light beard and wore a white shalwar kameez (traditional outfit) ... came walking toward our police and blasted himself," Malik said.
He later said authorities had found the head, whose "face was extensively damaged." It was being reconstructed by a plastic surgeon so police could release a sketch to the public, he said.
Malik confirmed that 18 people were killed. Naeem Iqbal, a police spokesman, said three of the dead were civilians and the rest were police officers.
At least two funerals were held in Islamabad and neighboring Rawalpindi, with mourners offering prayers in front of coffins draped in Pakistani flags and covered with flowers.
Relatives and friends hovered around the wounded in hospitals, kissing and embracing them as they recalled the attack.
"The noise was deafening. It still rings in my ears," said Kalim Ullah, a 24-year-old police officer who was wounded in the left leg.
The bombing was reminiscent of a suicide attack that killed 13 people and wounded 71 last July 27 - the day the Red Mosque reopened after a bloody commando assault on the compound. That explosion was at a restaurant crowded with police officers.
Sunday's attack also came after threats of revenge from Pakistani Taliban leaders angered by an offensive by a paramilitary force against insurgents in the Khyber tribal area along the border with Afghanistan.
The government elected in February parliamentary elections has sought to end militancy in Pakistan mainly through peace deals.
That approach has drawn criticism from U.S. officials, who say the deals will give pro-Taliban militants time to regroup.
The government siege at the Red Mosque began following tensions over the mosque's anti-vice campaign, in which bands of supporters harassed music shops and kidnapped alleged prostitutes.
The government said 102 people, including 11 security personnel, were killed during the eight-day standoff, but critics say far more people died, and the siege still resonates as a rallying cry among Islamic militants.
At the Red Mosque on Monday, supporters informally re-established a girls' seminary that was razed after the siege. About 25 girls in colorful head scarves sat cross-legged on mats on the ground where the school once stood, reciting the Quran.
People leaving the Red Mosque - now repainted beige - after afternoon prayers expressed distress over Sunday's bombing.
"It wasn't good what happened," said Bilal Kashmiri. "All people are dear to God."
