QUETTA, Pakistan (AP) — Gunmen killed 21 miners and wounded six others in Pakistan’s southwest, a police official said Friday, drawing condemnation from authorities as a search was launched for the assailants.

The latest attack in the restive Balochistan province came days ahead of a major security summit being hosted in the capital.

The gunmen stormed the accommodation at a coal mine in Duki district late Thursday night, rounded up the men and opened fire, police official Hamayun Khan Nasir said. He said the attackers also fired rockets, lobbed grenades at the mine and damaged machinery before fleeing.

Most of the casualties were from Pashto-speaking areas of Balochistan. Three of the dead and four of the wounded were Afghan. Angered over the violence, local shop owners pulled their shutters down to observe a daylong strike against the killings.

One of the critically wounded miners died later at a hospital, increasing the death toll to 21, Nasir said. However, he said the families of the killed miners for hours refused to bury them and staged a sit-in at the site of the attack in Duki.

Under Islamic tradition, burials take place as quickly as possible after death, but the demonstrators before ending the protest insisted they would not hold funerals until authorities arrest the killers, Nasir said.

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No group claimed immediate responsibility for the attack, but suspicion is likely to fall on the outlawed Baloch Liberation Army, which targets civilians and security forces.

The province is home to several separatist groups who want independence. They accuse the federal government in Islamabad of unfairly exploiting oil- and mineral-rich Balochistan at the expense of locals.

Foreign investors, many from China, have pumped billions of dollars in investment into Balochistan, but the separatists say few of the profits from development reach the local area.

The BLA launched multiple attacks in August that killed more than 50. They included 23 people, mostly from eastern Punjab province, who were fatally shot after being taken from buses, vehicles and trucks in Musakhail district in Balochistan. Authorities responded by killing 21 insurgents in the province.

Prime Minister Shehbaz Sharif expressed his deep sorrow over the coal mine killings and vowed to eliminate terrorism.

Sarfraz Bugti, the chief minister in Balochistan, said “terrorists have once again targeted poor laborers.” He said the attackers were cruel and had an agenda to destabilize Pakistan. “The killing of these innocent laborers will be avenged,” he said in a statement.

Interior Minister Mohsin Naqvi said those who killed the laborers would not be able to escape the grip of the law.

On Monday, the BLA said it carried out an attack on Chinese nationals outside Pakistan’s biggest airport. The bodies of the two slain Chinese engineers were sent to Beijing by a plane Thursday night, according to security officials.

There are thousands of Chinese working in the country, most of them involved in Beijing’s multibillion-dollar Belt and Road Initiative.

Two suspects linked to a 2021 bombing that killed nine Chinese nationals and four Pakistanis working on a dam in the northwest were killed Friday in eastern Pakistan, counterterrorism police said.

Police said the suspects died when armed men attacked a van transporting the suspects to a prison in Sahiwal, a district in Punjab province. No officer was harmed in the shootout, the statement from counterterrorism police said.

Sunday’s airport explosion, which the BLA said was the work of a suicide bomber, has raised questions about the ability of Pakistani forces to protect high-profile events or foreigners in the country.

Islamabad is hosting a summit next week of the Shanghai Cooperation Organization, a grouping founded by China and Russia to counter Western alliances.

Authorities have increased security in the capital by deploying troops and banning rallies.

However, Pakistan’s Tehreek-e-Insaf, the opposition party of imprisoned former premier Imran Khan, said Friday it would stage a peaceful protest in Islamabad on Oct. 15 when the two-day SCO summit begins in the city. Khan’s party wants his release. It also says Khan has been denied his right to meet with his legal team.

The Interior Ministry this week alerted provinces to take additional measures as separatists and the Pakistani Taliban could attack public places and government installations.

The killings of the miners came hours after Saudi and Pakistani businessmen signed 27 investment agreements valued at $2 billion across various sectors, including mining in Balochistan.

Saudi Arabia also wants to invest in Reko Diq, a district in Balochistan famed for its mineral wealth, including gold and copper.

Balochistan’s Gwadar Port is an anchor in the China-Pakistan Economic Corridor, part of Beijing’s Belt and Road initiative. The BLA has asked the Chinese workers to leave the province to avoid attacks.

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Associated Press writer Munir Ahmed contributed to this story from Islamabad.