Militants planted the explosive device in the Kurram Agency in Pakistan's Federally Administered Tribal Areas (FATA) bordering Afghanistan, said senior regional official Shahid Ali Khan.
"When the passengers were coming, they detonated the remote-controlled bomb," Khan, who is the assistant political agent for Kurram Agency, said.
Many of the 13 wounded were taken to hospital in the nearby town of Parachinar, Khan said. The military also sent a helicopter to evacuate the wounded to the key city of Peshawar.
A spokesman for the Jamaat-ur-Ahrar, a faction of Pakistani Taliban group, said the explosive device had been intended to target the country's Shias and workers in the area carrying out a census.
"Our target was the Shia community and census team in the area," said Asad Mansur, the spokesman.
Pakistan, a mainly Muslim nation of about 190 million people, is conducting a nationwide census but militants have frequently targeted officials collecting the data.
Four census officials were wounded in the blast, Khan added.
Prime Minister Nawaz Sharif ordered officials to "extend maximum support" for the treatment of the injured, his office said.
In January, a bomb planted in a busy vegetable market also killed 21 people.
Both blasts were claimed by the Pakistani Taliban terrorist group.
Since 2002, more than 2,600 Shi'ite Muslims have been martyred in sectarian attacks in Pakistan, data from the South Asia Terrorism Portal shows.