Quetta, Pakistan. Gunmen killed 20 miners and wounded another seven in Pakistan’s southwest, a police official said Friday, drawing condemnation from authorities as a search was launched for the attackers.

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

The gunmen stormed the accommodations at the 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 and lobbed grenades at the coal mine and damaged the machinery used for the mining before fleeing.

Most of the men attacked were from Pashtun-speaking areas of Balochistan. Three of the dead and four of the wounded were Afghan. Angered over the attack, local shop owners pulled their shutters down to observe a daylong strike against the killing.

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

Authorities say police and paramilitary forces are searching for the attackers.

The group committed multiple attacks in August that killed more than 50 people, while authorities responded by killing 21 insurgents in the province. Those killed included 23 passengers, mostly from eastern Punjab province, who were fatally shot after being taken from buses, vehicles and trucks in Musakhail district in Baluchistan.

Prime Minister Shehbaz Sharif expressed his deep sorrow over the 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 would be avenged,” he said in a statement.

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

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.

On Monday, a group called the Baloch Liberation Army 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.

The explosion, which the BLA said was the work of a suicide bomber, also 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 beefed up security in the capital by deploying troops to prevent any acts of terrorism.

The Ministry of Interior this week alerted the country's four provinces to take additional measures to enhance security as the separatist groups and Pakistani Taliban could launch attacks at public places and government installations.

The killings of miners came hours after Saudi and Pakistani businessmen signed 27 memorandums of understanding valued at $2 billion for investment across various sectors, including mining in oil and gas-rich Balochistan. Pakistan’s Prime Minister Shehbaz Sharif attended the signing of the memorandums in the capital, Islamabad.

Saudi Arabia also wants to invest in Reko Diq, district in Balochistan which famed for its mineral wealth, including gold and copper. Baluchistan’s Gwardar port is an anchor in the China-Pakistan Economic Corridor, part of Beijing’s vast Belt and Road infrastructure initiative, and BLA has asked the Chinese to leave the province to avoid attacks.