A suspected homicide bomber blew himself up inside a courtroom in troubled southwestern Pakistan on Saturday, killing a judge and 13 others, police and other officials said.

At least 25 people were injured in the attack, and some were in a critical condition, said city police chief Rauf Khan.

It was not immediately clear who was behind the attack at the District Courts complex in Quetta, the capital of southwestern Baluchistan province. Police were investigating.

"Civil judge Abdul Wahid has died in the bomb explosion," said Afaq Zahid, an area police chief, adding that the dead and injured had been taken to a hospital.

Khan said the blast killed 15 people, including Wahid, five lawyers and relatives of some of the prisoners on trial. He included the suspected attacker in the body count.

A senior intelligence official in Quetta, who spoke on condition of anonymity because he was not authorized to speak to media, said the attack was carried out by a homicide bomber.

"It was a suicide attack, and the head of the attacker has been collected," the intelligence official said.

Abdul Rashid, a lawyer who was in the complex but not the courtroom at the time of the blast, told The Associated Press that he saw a severed head inside the court. He speculated it might have been a homicide attack.

The blast shattered windows and destroyed furniture inside the courtroom. Shoes, strips of clothing and body parts littered the scene.

Police collected body parts, and bomb disposal experts were investigating to determine the exact nature of the attack, Khan said.

Pakistan's Interior Minister Aftab Khan Sherpao quickly condemned the blast, terming it "an act of terrorism."

Information was not immediately available about who was on trial and on what charges, at the time of the blast.

Shortly after the attack, lawyer and relatives of the dead and injured gathered outside the District Court complex and chanted anti-government slogans.

Hundreds of relatives thronged a main government hospital where the dead and injured were taken, according to witnesses, who said police were trying to pacify the emotional people.

More police patrols were immediately apparent on the streets of the city.

Pakistan is a key ally of the United States in its war on terror and has witnessed scores of terrorist attacks since it threw its support behind Washington following the Sept. 11, 2001, attacks in America.

The latest attack came a day after police announced that they had arrested five suspected militants from the southern city of Karachi and Rawalpindi, a garrison city near Islamabad, and that the suspects were planning homicide attacks on foreigners and minority Shiite Muslims.

Baluchistan has also been the scene of scores of rocket and bomb attacks, most blamed on nationalists, who have been pressuring the central government for more royalties for gas extracted in the province.

Authorities have recently arrested hundreds of suspected Taliban in Quetta and elsewhere as part of a campaign aimed at deporting Afghans living in Pakistan without valid travel documents.