"Six unidentified gunmen riding on two bikes opened fire at three Nato trailers at Kambri Bridge area near Sibi, said Levies Force sources adding that after firing, the assailants set the trailers on fire.

Later, the attackers managed to escape.

Levies Force immediately reached the place and cordoned off the entire area to trace out the attackers.

The incident caused suspension of traffic on Karachi-Quetta national highway for an hour, however, later, it was cleared.