At least 16 people were killed and four others critically injured in an attack on two passenger vehicles by militants on Saturday morning in Kurram Agency in Pakistan's northwest tribal area, reported local media.

According to the report, the attack took place early Saturday morning when some unknown gunmen opened fire at a caravan, comprising two passenger vehicles heading to Peshawar from Para Chanar, central place in Kurram Agency.

Five people died on the spot and some injured died on the way while being rushed to hospital, said hospital sources, adding a few more injured died of their critical wounds at hospital.

The militants fled the scene after indiscriminately firing at the vehicles with automatic weapons, leaving two vehicles riddled with bullets.

A local official MNA Sajid Hussain Toori termed the incident as an open terrorist attack, calling on the government to step up security measures for public at roads and open markets.

No group has claimed the responsibility for the attack.