Militants wearing security force uniforms stopped two buses in southwest Pakistan on Thursday and killed 14 passengers after ordering them out of the vehicles, police said.

Balochistan provincial police chief Mohsin Ali Butt told CNN that 15 to 20 attackers stopped the buses near the town of Ormara, in the south of the province.

The militants ordered 14 out of the total passengers to disembark and shot them at close range before escaping. "This was an act of targeted killing," he said.

An alliance of Baloch separatists, Baloch Raaji Aajoi Sangar (BRAS), claimed responsibility for the killings, saying in a statement sent to journalists that they had targeted passengers who were part of the country's military.

In the statement a BRAS spokesman said: "Those who were killed carried identity cards of the Pakistan Navy and Coast Guard, and were killed after being identified."

The buses were en route from Pakistan's largest city Karachi to the port city of Gwadar. Police and other government agencies have launched an investigation into the killings, Butt said.

Prime Minister Imran Khan expressed sympathy to families of the victims and vowed maximum efforts "to bring the perpetrators of the barbaric act to justice."

Restive province

The bus killings happened just days after a bomb claimed by a Sunni Muslim militant group ripped through a fruit market in the Balochistan city of Quetta, killing 20 people.

The attack last Friday hit the city's Hazarganji district, which is home to a large community from the Hazara Shia Muslim minority. Lashkar-e-Jhangvi, a Sunni militant group known to target Hazaras, said it was responsible.

In December 2017, a suicide bomber attacked a church packed with worshipers in Quetta, leaving seven people dead. Just months later, another bomber attacked police and troops in the city, killing six officers and injuring eight.

In July last year, 149 people were killed and 186 injured in a suicide attack in the Mastung area south of Quetta, which targeted the convoy of a political candidate.

ISIS claimed responsibility for that bombing, the second deadliest terror attack in Pakistan's history.