Heavily armed militants looted several banks in Pakistan's Balochistan province on Monday before clashing with security forces, with one policeman and a civilian killed, authorities told AFP.

No one has claimed responsibility for the attack in southwest Pakistan, where ethnic Baloch separatists have stepped up attacks on security forces in recent years.

"It was an organised heist in which at least three banks were looted of about 150 million Pakistani rupees (around $530,000)," a police official in the Panjgur district said.

"They tried to loot two more banks before clashes erupted with security forces, forcing them to flee," he said, speaking on condition of anonymity as he was not authorised to talk to the media.

At least one officer was killed and two others were wounded, while a shopkeeper was killed in the crossfire, the official told AFP.

A senior administration official in the district confirmed the attack, adding that 50 to 60 militants arrived via 12 motorcycles and four vehicles.

"They were separatists from the Baloch Liberation Army (BLA)," he told AFP, requesting anonymity.

Balochistan is Pakistan's largest and most resource-rich province, but also its poorest.

The BLA is one of several ethnic and sectarian militant groups active in the region.

The BLA, designated a terrorist organisation by Pakistan, the United States and other countries, has emerged as the biggest threat to foreign interests while also targeting security forces and Pakistanis outside the province.

In March, the group seized a train carrying more than 450 passengers, resulting in a two-day siege that left dozens dead.