The Jamaat-ur-Ahrar said it detonated the remote-controlled explosive device on Tuesday in FATA's Mohmand about 170 km (105 miles) from Islamabad.
Blast kills 2 US mission staffers in Mohmand
"Jamaat-ur-Ahrar's mujahideen carried out a remote-controlled bomb attack that sent a FATA secretariat employee and his driver to hell," said a statement emailed to Reuters.
Faisal Khan and Abid Shah were killed while on a drug eradication mission, the US State Department said.
Khan was identified by US authorities as the most senior Pakistani employee at the US Consulate in Peshawar. Shah was identified as the driver, having joined the consulate in 2009 as a security specialist.
Four other Pakistanis were wounded in the blast, the Taliban said.
Pakistan's volatile tribal areas have been home to an insurgency by Islamist militants under the banner of TTP since 2007.
The tribal areas, including Mohmand, have seen multiple rounds of military operations reduce the TTP's capacity, but targeted attacks against state and civilian targets are common.
Two killed in Mohmand Agency IED blast
Mohmand has seen increasing violence in recent weeks. On February 18, Jamaat-ur-Ahrar gunmen killed nine Pakistani paramilitary soldiers in two separate attacks.
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