Separatist gunmen shot and killed at least 22 people in southwest Pakistan on Monday in an attack that singled out ethnic Punjabis, government officials said.

Dozens of militants carried out the shootings early Monday in the district of Musakhail in impoverished Balochistan province, where security forces are battling sectarian, ethnic and separatist violence.

The Baloch Liberation Army (BLA), the most active militant separatist group in the province, claimed responsibility for the attack -- one of the worst shootings in the region in the past several years.

The perpetrators stopped buses, vans and trucks one after the other on a highway connecting Punjab with Balochistan, Najibullah Kakar, a senior official in Musakhail, told AFP.

"The numbers of the militants were between 30 to 40. They stopped 22 vehicles," he said.

"Vehicles travelling to and from Punjab were inspected, and individuals from Punjab were identified and shot."

He said 22 people were killed, mostly Punjabi labourers, as well as two paramilitary soldiers.

Hameed Zehri, another senior official in the district, confirmed the death toll to AFP.

Balochistan is Pakistan's poorest province, despite an abundance of untapped natural resources, and lags behind the rest of the country in education, employment and economic development.

Baloch separatists have in recent years intensified attacks on Pakistanis from neighbouring provinces working in the region, as well as foreign energy firms they believe are exploiting its riches.

Punjabis are the largest of the six main ethnic groups in Pakistan, and are perceived as dominating the ranks of the military, which is locked in a battle to quash Balochistan's armed factions.

In a statement to AFP, the BLA said without providing evidence that those shot were military servicemen in civilian clothes who were "identified and subsequently killed by BLA fighters".

An earlier statement by the group published just after midnight on Monday warned the Baloch public to stay away from the highway, adding that their "fight is against the occupying Pakistani military".

"We have taken full control of all major highways across Balochistan, blocking them completely," it added.

Surge in violence 

The BLA mostly targets security forces, and attacks on civilians often go unclaimed.

In a similar attack in April, 11 Punjabi labourers were killed when they were abducted from a bus in the city of Naushki, and six Punjabis working as barbers were shot in May.

In February, on the eve of national elections, twin blasts in the province killed 28 people and were claimed by the local chapter of the Islamic State group.

Protests led by ethnic Baloch are staged regularly in the province accusing the authorities of a heavy-handed crackdown in its fight against militancy, including through mass arrests and detentions.

Pakistan witnessed a surge in militant attacks since the Taliban government returned to power in neighbouring Afghanistan in 2021, mostly in the northwestern border province of Khyber Pakhtunkhwa, but also in southwestern Balochistan, which abuts Afghanistan and Iran.

There were at least 170 militant attacks killing 151 civilians and 114 security personnel in Balochistan last year, according to the Pakistan Institute for Conflict and Security Studies.

Islamabad accuses Kabul's new rulers of failing to root out militants sheltering on Afghan soil as they prepare to stage assaults on Pakistan.

Prime Minister Shehbaz Sharif expressed "deep grief and condemnation over the terrorist attack" in a statement issued Monday by his office.