Pakistani police say they are detaining suspected militants in connection with an attack on a Shiite mosque, which killed at least 47 people. But authorities have not ruled out foreign involvement.
Police in the southwest Pakistan city of Quetta say they have taken at least 15 suspected Sunni Islamic militants into custody for questioning.
No group has claimed responsibility for the attack on a Shiite mosque, but the incident is being described as an act of sectarian violence by Sunni extremists.
While the Sunni majority and Shiite minority generally live together peacefully, violence between the two groups has plagued the country for decades.
In addition to questioning local militants, Pakistan President Pervez Musharraf said authorities are also investigating whether the attack is the work of foreign terrorists. "The possibility of any across-the-border involvement cannot be ruled out. We need to see, and we will have to take stern action whatever the cause," Mr. Musharraf said.
Quetta lies near the border with Afghanistan, where remnants of the ousted Taleban regime are reportedly still operating.
The attackers opened fire on the Shiite worshippers as they began their Friday prayers.
Two of the assailants then reportedly blew themselves up, and the incident is now officially said to be a suicide attack. Another attacker was captured but later died of his wounds, while an unknown number of assailants have fled.
The killings sparked violent demonstrations by Quetta's Shiites, prompting the government to declare a curfew.
The authorities relaxed the curfew Sunday, as calm returned to the city.
Prime Minister Zafarullah Jamali has promised government compensation payments for the victims' family members.