An injured police officer, second from right, is helped by his colleagues at the site of a bomb explosion in Islamabad, Pakistan on Friday, July 27, 2007. [AP]

ISLAMABAD, Pakistan - A suspected suicide bomber killed at least 13 people at a hotel Friday after hundreds of stone-throwing protesters clashed with police as the capital's Red Mosque reopened for the first time since a bloody army raid ousted pro-Taliban militants holed up there.

The blast, targeting police, was the latest in a string of militant revenge attacks and deepened the security crisis facing President Gen. Pervez Musharraf, a close U.S. ally.

The bombing comes on the back of almost daily suicide blasts in Pakistan's restive northwestern frontier, where Musharraf is also under U.S. pressure to crack down on al-Qaida. More than 300 people have died in violence which began with the siege of the Red Mosque at the start of July.

Interior Ministry spokesman Javed Iqbal Cheema said the government had received intelligence about a possible suicide bombing in the Aabpara market where the attack happened about 5:15 p.m. Friday. He said there would be an official inquiry into the security lapse, but he also blamed the mosque unrest for creating the conditions in which an attacker could strike.

"If these people had not created such a situation, it would not have happened," he said, adding the mosque was now indefinitely closed.

Authorities had hoped to restore normalcy to the once-staid Pakistani capital by reopening the Lal Masjid, or Red Mosque, to the public more than two weeks after the commando raid dislodged militant supporters of its pro-Taliban clerics.

But religious students, angered by the government's move to assign a cleric from another mosque to lead Friday prayers, staged protests inside the Red Mosque's compound and occupied it for several hours.

They daubed red paint onto the walls and dome to restore its namesake color after a government restoration left it pale yellow. They also put up a black flag with two crossed swords ¡ª meant to symbolize jihad, or holy war. Street battles then broke out between stone-throwing protesters and police using tear gas.

Soon after came a thunderous blast in an open-air restaurant at the Muzaffar Hotel, located in a crowded market district about a quarter-mile away from the mosque.

Cheema said it was a "pre-planned bombing" targeting police.

"It was a huge explosion," said witness Mohammed Ali. "There were policemen sitting and standing at the restaurant, and the explosion occurred after someone came near them," he said, his shirt stained from the blood of victims he helped carry to ambulances.

"A policeman got blown into the air and landed away from the blast site," said another witness, Imtiaz Ahmed.

Television footage showed rescuers rushing bodies from the scene, many bleeding and others partially stripped of their clothes and with skin blackened and raw from the blast.

Khalid Pervez, Islamabad's top administrator, said 13 people were killed, including seven police, and 71 were wounded, mostly bystanders.

Cheema said investigators had also recovered a head believed to be that of the attacker.

There was no claim of responsibility for the bombing, but Islamic militants were strongly suspected. It was the second major bombing to hit this city in 11 days. A July 17 suicide attack killed 16 people at a planned rally for the country's top judge.

Prime Minister Shaukat Aziz condemned the latest attack and said it would not deter the government's resolve to fight terrorism, the state Associated Press of Pakistan reported.

Islamabad had been gradually recovering from the mosque siege that left at least 102 dead, although security forces are still deployed at sandbagged bunkers on street corners.

Authorities had repaired the blast-scorched interior of the mosque, its damaged minarets and the bullet-riddled roof over its entrance hall.

But hopes that reopening the mosque would cool public anger over the siege ¡ª amid lingering skepticism over the official death toll ¡ª were dashed.

Bearded religious students and other hard-liners who gathered for prayers soon began chanting anti-government slogans and took control of the mosque compound.

"Musharraf is a dog! He is worse than a dog! He should resign!" students shouted.

They demanded the mosque's former chief cleric, Abdul Aziz, be allowed to lead the prayers. Aziz was caught trying to escape the mosque compound during the siege wearing a woman's burqa. He is currently in government detention.

The crowd also shouted support for Aziz's brother, Abdul Rashid Ghazi, who led the siege until he was shot dead by security forces after refusing to surrender. He had spearheaded a vigilante, Islamic anti-vice campaign that had challenged the government's writ in the city.

"Ghazi, your blood will lead to a revolution," the protesters chanted.

Maulana Ashfaq Ahmed, the senior cleric whom the government had asked to lead the prayers, was quickly escorted from the mosque, as protesters waved angry gestures at him.

In a speech at the main entrance of the mosque, Liaqat Baloch, deputy leader of a coalition of hard-line religious parties, the Mutahida Majlis-e-Amal, condemned Musharraf as a "killer."

"Maulana Abdul Aziz is still the prayer leader of the mosque. The blood of martyrs will bear fruit. This struggle will reach its destination of an Islamic revolution. Musharraf is a killer of the constitution. He's a killer of male and female students. The entire world will see him hang," Baloch said.

Unrest later broke out on the street outside, as protesters confronted scores of riot police backed by armored personnel carriers. Police were armed, but there was no gunfire or reports of serious injuries.

After the bombing, police retook control of the mosque, said Zafar Iqbal, the city police chief. Some protesters resisted and about 50 people were arrested, he said.

Wahajat Aziz, a government worker who was among the protesters at the Red Mosque, said officials were too hasty in reopening the mosque.

"They brought an imam that people had opposed in the past," he said. "This created tension in the environment. People's emotions have not cooled down yet."