ISLAMABAD — Thirty-five people were killed Saturday in an inferno that engulfed two oil tanker trucks and two passenger buses after a collision in south-western Pakistan, officials said.A bus bound for Karachi collided with one of the tanker trucks coming from the opposite direction and then both hit the two other vehiclesand all caught fire, police official Ahmed Nawaz said.The collision occurred on a coastal highway in the Gaddani area of Balochistan province, said Jan Muhammad Buledi, a spokesman for theprovincial government.At least 20 people were injured in the accident, Buledi said.Some of the bodies were charred beyond recognition and DNA testing was being conducted to ascertain their identities, said a doctor atthe civil hospital in Karachi.Buledi said the buses caught fire because they were carrying canisters of smuggled Iranian gasoline and diesel on top of them.Poor road infrastructure, poor road safety standards and weak laws to regulate traffic cause thousands of deaths in traffic accidents in Pakistan each year.