A bomb ripped through a government official's house in northwestern Pakistan on Sunday, killing him and his five family members in an attack that police said was in retaliation for military operations targeting Taliban in the area.

The military has stepped up airstrikes in Kurram since many militants fled there following a major ground offensive launched in nearby South Waziristan in mid-October. Both areas are in Pakistan's lawless tribal region near the Afghan border.

Sunday's attack targeted the house of Sarbraz Saddiqi, a government official in Kurram, said police officer Naeemullah Khan. The dead included Saddiqi, his wife and four children, he said.

Police are investigating how the bomb was planted in Saddiqi's house and whether it was detonated by timer or remote control, said Khan.

The attack appeared to be in retaliation for the military's stepped-up effort to target Taliban militants in the area who have fled from South Waziristan, said Khan. Government officials have also been kidnapped in Kurram, he said.

Many Taliban militants are also believed to have fled to North Waziristan, an area in Pakistan's tribal region dominated by jihadi groups launching cross-border attacks against coalition forces in Afghanistan.

Washington has pressed Pakistan to target such groups but has received a reluctant response, as Islamabad has continued to concentrate on militants that pose a domestic threat.

The U.S. has responded by relying more heavily on drone missile strikes in Pakistan's tribal areas, including one Saturday in the Babar Raghzai area of North Waziristan.

Pakistani intelligence officials on Sunday raised the death toll from the strike to 13 after eight more bodies were pulled from the rubble and two wounded died in the hospital.

The U.S. rarely discusses the covert program but has in the past said it has taken out several top Al Qaeda operatives.

At least one local militant commander was killed in Saturday's strike. But authorities were still trying to determine how many of the others were militants or civilians, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

Pakistan publicly opposes the strikes but is believed to secretly aid them.