Pakistani officials on Monday said at least 23 people were killed in a militant attack on a highway in southwestern Pakistan which targeted vehicles from buses to goods trucks.

Armed men blocked the route in the province of Balochistan on Sunday night, took passengers off the vehicles, and shot them after checking their identity cards, a senior superintendent of police, Ayub Achakzai, told reporters.

"The armed men also not only killed passengers but also killed the drivers of trucks carrying coal," said Hameed Zahir, the deputy commissioner of the area where the incident occurred.

At least 10 trucks were set on fire after their drivers had been killed, he added.

Militants fighting a decades-old ethnic insurgency to demand the secession of resource-rich Balochistan from Pakistan have targeted workers from the eastern province of Punjab whom they see as exploiting their resources.

In a statement, the Balochistan Liberation Army group said its fighters had targeted military personnel travelling in civilian clothes, who were shot after being identified.

Pakistan's interior ministry said the dead were innocent citizens.

The office of Prime Minister Shehbaz Sharif condemned the attack in a statement, vowing that security forces would retaliate and bring those responsible to justice. (Reuters)