ISLAMABAD, Pakistan (CNN) -- At least 12 people were killed when a suicide bomber attacked the site where the country's suspended chief justice was scheduled to address a rally, sources in Pakistan told CNN.
An ambulance arrives on the scene of a blast that killed at least 12 people in Islamabad, Pakistan, on Tuesday.
Along with the dozen killed, at least 35 others were wounded in the blast Tuesday, hospital sources said.
Recent events at Islamabad's Red Mosque have heightened tensions in Pakistan and triggered a wave of violence.
Militants and radical students holed up in the mosque two weeks ago after a battle with police. The situation turned into a bloody military siege in which dozens of people were killed.
The latest attack occurred at the site of a planned rally for the country's suspended chief justice, Iftikhar Mohammed Chaudhry. Watch explosion shock festive rally crowd »
A bomb exploded 50 meters (50 yards) away from the rally stage before the event started. Chaudhry had not arrived at the scene when the explosives detonated.
Chaudhry was removed from office on March 9 by President Pervez Musharraf, who accused Chaudhry of misusing his powers.
The dismissal sparked widespread, largely peaceful demonstrations by the country's attorneys and those who believe Musharraf abused his authority in suspending Pakistan's top judge.
Musharraf appointed Chaudhry to the court in 2005, but the judge fell from favor after he started exercising independence from the government in a number of cases involving the disappearance of terrorist suspects and human-rights activists.
Pakistan has been wracked by other violence.
A series of bombings in recent days in northwestern Pakistan, after the collapse of a truce between the government and tribal militants, has been spreading fears in the region and the West.
Attacks since late last week, targeting Pakistani military and police, have killed at least 79 people, authorities said.
Militants linked to the Taliban in the area near the Afghan border said the truce reached with the Pakistani government last September is off.
That deal has been blamed for an increase in attacks on U.S. troops over the border in Afghanistan, as Taliban fighters were able to prepare, train, and rebuild weapons supplies without interference from the Pakistani government.
The Taliban is the former Afghan regime that sheltered al Qaeda until the U.S.-led war following the September 11, 2001, terror attacks.
Now, U.S. intelligence officials say al Qaeda has established a "safe haven" in Waziristan, just over the border into Pakistan, and that Osama bin Laden is believed to be in the area. E-mail to a friend
CNN's Mohsin Naqvi contributed to this report.