A suicide bomb attack in a restaurant near Islamabad's Red Mosque complex today killed at least 13 people, a majority of them police, and wounded 50, officials said, warning they could not rule out more attacks.
The mosque had been the centre of a protest by Islamist radicals earlier in the day.
Javed Iqbal Cheema, interior ministry spokesman, told a news briefing: "The suicide bomber entered the resturant and blew himself up among policemen. Police were the target."
"The head of the bomber has been found."
Khalid Pervez, the top administrator in the city, said the authorities had information that more suicide bombers had sneaked into Islamabad.
"We had taken all precautionary measures but despite that this unfortunate incident took place. Such attacks cannot be ruled out in future as well," Mr Pervez said.
Pakistan has suffered a spate of suicide attacks by Islamist militants since a military operation to crush a Taliban style movement at the Red Mosque, or Lal Masjid, earlier this month.
Over 180 people have been killed, mostly police and soldiers, in the attacks aimed at destabilising the government of President Pervez Musharraf.
At least seven police were killed in the latest blast, Interior Secretary Kamal Shah told Reuters, adding that it was probably retaliation for the assault on the Red Mosque.
The bombed restaurant was located some 550 metres from the mosque. Police caps and clothing lay at the blast site, which was spattered with blood.
A witness, Nisar Ahmed, said: "It was a very big blast. I myself saw two bodies flying into air and falling on the road."
After the blast police in the vicinity were told by other officers using megaphones not to let any strangers near them.
Earlier Pakistani police had fired tear gas to disperse protesting Islamists who had spoiled government plans for the resumption of religious activities at the mosque complex, which had been a battleground earlier this month.
Pakistani security forces stormed the Red Mosque compound on July 10 following a week-long siege after supporters of radical clerics there refused to surrender.
The government said 102 people were killed in the assault on the compound, the base for a Taliban-style movement.