A judge and six lawyers were among 15 people killed in a suspected suicide bomb attack on a courtroom in the southwestern Pakistani city of Quetta today.
The bomb exploded while a court was in session, police in the capital of Baluchistan province said.
At least 25 people were injured and police chief Rahu Khan Brohi said six of them were in a critical condition.
Police were stopping and questioning drivers of cars and trucks at road blocks set up in Islamabad, and foreign embassies have told their staff to limit their travel in the capital.
Officials were unsure whether the blast at a lower court in Quetta was carried by the Taliban or by ethnic Baluch militants fighting for greater autonomy.
"Initially we suspect nationalist extremists, as well as Afghan Taliban could be behind the attack," Razak Bugti, a spokesman for the Baluchistan government, said.
Pakistan is in the midst of a security scare after a spate of suicide attacks that intelligence officials have linked to groups operating from tribal areas, regarded as hotbeds of support for the Taliban and militants linked to al Qaeda.
Police found a head amongst the carnage, raising suspicions that the blast could be have caused by a suicide bomber, Rehmat Niazi, the police officer in charge of operations, said.
The upward force of a blast from a suicide belt typically decapitates the bomber.
"We're looking into the possibility of whether it was a suicide attack," Mr Niazi said.
Television footage from the wrecked courthouse showed people and police walking through pools of blood, collecting belongings. Body parts and torn clothes could be seen all around.
An outbreak of suicide attacks in Pakistan followed an army air strike on a militant base in South Waziristan tribal region in mid-January.
Nearly 30 people have been killed in the blasts, and attacks in the capital Islamabad and northwest city of Peshawar raised fears that militants were retaliating by targeting cities, in order to weaken President Pervez Musharraf's resolve.