At least 18 security personnel and two civilians died in the blast, Khan said.
About eight vehicles were destroyed in the attack and a nearby building housing troops and police was badly damaged.
The attack was condemned as a "cowardly act of terrorism" in a statement from the office of Yousuf Raza Gilani, the prime minister, which added that the government would use an "iron hand" against opposition fighters.
The checkpoint is near the Orakzai tribal region in Pakistan, which has emerged in
recent months as stronghold for pro-Taliban fighters who have stepped up their battle against the government.
Western nations are pressing Pakistan to take greater action against pro-Taliban forces and al-Qaeda elements in the tribal areas bordering Afghanistan.