Three more police officers have died from the suicide attack near Islamabad’s Red Mosque, bringing the death toll to 18, an official said Monday.

Naeem Iqbal, a police spokesman, said two officers died late Sunday from their wounds, while the third died early Monday.

No one has claimed responsibility for the explosion, which also wounded dozens and appeared to be the capital’s deadliest in about a year. Three of the dead were civilians while the rest were police, Iqbal said.

The blast unnerved the usually tranquil city the same day thousands of Islamists marked the one-year anniversary of a military siege on the nearby radical Red Mosque, an event that had prompted a massive police presence in the area.

Politicians, including President Pervez Musharraf and Prime Minister Yousuf Raza Gilani decried the attack, one of many in Pakistan that have victimized security forces.

“This is against humanity,” Gilani told reporters Monday after visiting some victims at an Islamabad hospital. “The law will take the culprits in its grip.”

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 it also promised to raise more concern about government moves to strike peace deals with militants.

Hours after the blast, Interior Ministry chief Rehman Malik told Geo TV that a teenage boy was the suspected attacker, though earlier he said it was a man apparently in his 30s.

“All witnesses say that a 15- or 16-year-old boy, who had a light beard and wore a white shalwar kameez ... he came walking toward our police and blasted himself,” Malik said.

Malik also initially said authorities found the “upper part” of the attacker’s body, but later he said two torsos found were identified as belonging to police. Malik also told Geo that components of a suicide jacket were recovered.

About a dozen investigators milled about the scene Monday, some poking around the grass with sticks, others looking at police gear scattered on the ground. Barbed wire, yellow tape and metal roadblocks sectioned off the area, and rain had washed away much of the splattered blood.

Musharraf urged resilience following the blast.

“The crisis we are going through at this time, it is so serious that if we do not control ourselves, it can get even more serious and perhaps we then not be able to control it then,” said the embattled president, whose alliance with the U.S. in the war on terror has been blamed by many Pakistani for fueling violence in their country.

It was not clear if the attack was linked to the conference held Sunday to remember last July’s military siege of the Red Mosque, and a mosque official condemned the assault.

“This is a very tragic and condemnable incident,” mosque spokesman Mohammed Amir Siddiq told The Associated Press.

The government launched the siege 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 in the eight-day standoff and the siege still resonates as a rallying cry among militants.

Sunday’s blast was eerily reminiscent of a suicide attack that killed 13 people and wounded 71 on July 27, 2007 _ the day the Red Mosque first reopened after the military operation. That explosion was at a restaurant crowded by police guarding the reopening.

The attack Sunday also came after recent threats of revenge from Pakistani Taliban leaders angered by a paramilitary operation against insurgents in Khyber tribal area in the northwest.

Levels of violence have fallen in Pakistan since last year, but attacks still occur in the country as resentment continues in many corners against the country’s partnership with the U.S. in the war on terror.

A new government that came to power following February elections has sought to end militancy in Pakistan primarily through peace deals with extremists. That approach has earned criticism from U.S. officials, who say the deals will simply give time for pro-Taliban militants to regroup and intensify attacks on foreign forces in neighboring Afghanistan.

However, the government shifted from its strategy in late June, as militants in Pakistan’s northwest increasingly began threatening the key city of Peshawar. The government launched a paramilitary operation in Khyber to flush out the extremists.

That operation has now been halted while officials try to negotiate peace through tribal elders, but Pakistani Taliban leaders have vowed revenge for the government’s show of force.

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Associated Press Writer Nahal Toosi contributed to this report.