"They fired indiscriminately at the vehicle, killed a policeman and fled," an intelligence official said.
Tank adjoins South Waziristan where a Pakistani air raid on a suspected Taliban and al-Qaeda base this month killed up to 20 people.
Tensions
In another incident, activists attacked a tribal police post in Bajaur, the most northern district of Pakistan's federally administered tribal areas, with rockets and machinegun fire on Thursday night, critically wounding a policeman.
Hundreds of people have been killed in Waziristan, a mountainous region of Pakistan bordering Afghanistan, in clashes between security forces and activists since the end of 2003.
The region has been relatively calm since the government agreed peace deals with activists in 2005 and last year, but US officials said cross-border incursions into Afghanistan have increased significantly in recent months.
Tensions rose in the federally administered tribal areas after the South Waziristan air raid and tribal officials fear a breakdown in peace accords.
Four soldiers and a woman were killed in a rare suicide car bomb attack in neighbouring North Waziristan this week.