Militants bombed the residence of a senior security official for the second time in two weeks Monday, this time in an attack that killed at least eight people in the sprawling southern seaport of Karachi.

The apparent target of the suicide truck bombing Monday, a top investigator in a unit charged with cracking down on militants in Karachi, was unharmed, and he spoke defiantly to reporters at the scene.

“If they are man enough, they should come and attack me out on the streets,” Chaudhry Aslam said, according to the television news channel Express 24/7. The Pakistani Taliban asserted responsibility for the bombing.

Twelve days ago, two suicide bombers struck the home of a senior army official in the southwestern city of Quetta, killing at least 23 people. The Pakistani Taliban, a homegrown militant outfit based in the nation’s mountainous tribal region, also asserted responsibility for that attack, saying it wanted to avenge the recent arrest of an al-Qaeda leader in Quetta.

The Pakistani Taliban functions as a sort of umbrella organization of insurgents who seek to overthrow the Pakistani state. It regularly attacks military and police installations and checkpoints, as well as civilian gathering spots. The two attacks on senior security officials’ houses are a new tactic, which one top Karachi police official described to reporters as “unexpected.”

Karachi is a teeming city of 18 million that is engulfed in an increasingly deadly spiral of gang warfare. Political parties, which stoke ethnic tensions in the city, are widely thought to be affiliated with heavily armed mobs that are vying for turf and votes. Al-Qaeda and Taliban militants also use the city to raise money and to hide, security officials say.

“We will continue targeting all such officers who are involved in the killing of our comrades,” a Taliban spokesman, Ahsanullah Ahsan, told the Associated Press.

Police said Monday’s suicide bomber detonated a white van laden with explosives outside Aslam’s residence in Karachi’s Defense neighborhood, an upscale district that is normally fairly immune from the city’s violence.

The van exploded just before children were to arrive at a nearby school, whose windows were shattered. In addition to six police officers, a teacher and her son were killed, officials said.

“This is not a matter of a security lapse,” the provincial home minister, Manzoor Wasan, told reporters at the scene. “This is a war that has gripped the entire country.”