Islamabad police on Sunday detained more than 200 people, a day after a blast at a restaurant in Islamabad killed one Turkish woman and wounded 11 people, eight of them foreigners, an official said.
Police Chief Shahid Nadeem Baloch said among the detained are madrassa students "who are suspected of having links with banned extremist organizations," and Afghan refugees.
Baloch told DPA the Federal Investigation Agency will work with Islamabad police in the inquiry.
Earlier, Interior Secretary Kamal Shah said the blast at the Luna Caprese Italian restaurant Saturday night was not a suicide attack, but resulted from a device apparently planted outside the restaurant.
The US embassy Sunday urged Americans to avoid areas where Westerners congregate.
US Embassy spokeswoman Kay Mayfield confirmed there were "both official and private sector Americans injured," but said she could not give numbers.
A spokesman for Poly Clinic where most the wounded were taken said they included five Americans, one Japanese, one Canadian, and one British citizen.
President Pervez Musharraf condemned the blast and said it cannot break the government's resolve to fight terrorism, his spokesman told reporters.
Pakistan has suffered more than 60 suicide attacks in the past 15 months that have killed more than 1,000 people.
The latest attacks have been in Lahore, but overall most of the attacks have occurred in the volatile tribal areas of the North-West Frontier Province (NWFP).
Pakistan's tribal areas are safe havens for a Al Qaeda militants and Taliban fighters who have launched cross-border attacks on international forces into Afghanistan.
However, the militants have turned inward and launched regular attacks against Pakistani security forces and rival tribes.