A suicide bomber blew himself up in a courthouse in southwestern Pakistan, killing 15 others, including a judge, in the deadliest of a series of attacks that have struck the country in recent weeks. There is suspicion in Pakistan that pro-Taliban militants are targeting sensitive sites to undermine the country's support of the United States, and an official in the region where Saturday's attack took place hinted at Afghan involvement. The explosion wounded 24 people and left bloodied clothes and body parts scattered next to wrecked furniture and shattered glass in Quetta District Courts. It forced police - already on alert - to further tighten security nationwide. "Afghans have been involved in previous such attacks here. I cannot rule out their involvement in today's attack, but we don't have any evidence to prove it," Jam Mohammed Yousaf, the top elected official in Baluchistan, told reporters in Quetta on Saturday. Relations between the neighboring countries have soured over Afghan allegations that Pakistan is supporting Taliban militants who have escalated their campaign of violence in the neighboring country over the past year. Pakistan denies helping the militants but acknowledges that some operate from its soil. Increasingly, it appears Pakistan itself has become a battleground. There have been about 10 bombings in the past month, mostly in the tribal northwest, but the capital Islamabad has also been targeted in suicide attacks at its international airport and the Marriott Hotel. Saturday's blast in Quetta, a city where Taliban activists and leaders are alleged to hide, was by far the deadliest. The suicide bomber "entered the courtroom on foot and he immediately exploded himself," Yousaf said. The blast killed Judge Abdul Wahid, five lawyers and some of the relatives of prisoners who were on trial, Yousaf said. He could not give details about the prisoners' identities or the cases being heard. The attacker died, along with 15 others. Mohammed Aziz, 20, who had come to the courts complex for a trial involving a cousin, was standing near the scene of the attack and was knocked over by the blast. "The deafening explosion happened when I was standing near the courtroom. I don't know who did it, but I did hear cries and something hit my face and chest, and I fell on the ground," he said from his hospital bed, where he was recovering from burn injuries. He was still unsure if his cousin had survived. Shortly after the attack, a crowd angered by the lapse in security gathered outside the court complex and chanted anti-government slogans. Hundreds of relatives later crowded a government hospital where the dead and wounded were taken to find out the fate of loved ones. Prime Minister Shaukat Aziz - who was visiting the northwestern city of Peshawar on Saturday to meet with families of some police officials who died in an earlier suicide attack - condemned the bombing. "It is an attack on humanity," he said. The Quetta attack came a day after police near Islamabad and southern city of Karachi said that they had arrested five militants who were allegedly planning suicide attacks on foreigners and minority Shiite Muslims. Also, police in the southern city of Sukkr said Saturday they had arrested three militants planning suicide attacks at upcoming Shiite gatherings.