QUETTA, Pakistan, Oct 11 (Reuters) - Unidentified gunmen

attacked a cluster of small private coal mines in southwestern

Pakistan early on Friday, shooting some miners as they slept and

lining up others before opening fire, killing 21 in the restive

region, police said.

The attack by 40 armed men days before Pakistan hosts a

summit of the Shanghai Co-operation Organization grouping is the

worst in weeks in the mineral-rich province of Balochistan

bordering Afghanistan and Iran.

"The armed terrorists remained for around 1-1/2 hours in the

mining area," regional police official Asif Shafi told Reuters.

"They fired rockets and hurled grenades at the mines and miners'

quarters."

There was no immediate claim of responsibility for the

attack on the mines of the Junaid Coal Co in the Duki area,

which injured six. Among the dead were four Afghan nationals and

another four were injured.

Businesses and shops were shut in Duki as hundreds of people

gathered along with the bodies of the dead in a protest to

demand the arrest of the attackers, police said.

"We were receiving threats from the militants for some time

but there was no information about the attack," said mine-owner

Khairullah Nasar, who is also the chairman of the district

council.

The attackers burnt down all 10 mines, along with the

equipment and machinery within, he added.

A decades-long insurgency in Balochistan has led to frequent

militant attacks against the government to press demands for a

share of regional resources.

Several attacks have targeted migrant workers, including

some from Afghanistan, employed by smaller, privately operated

mines.

The government was "determined to root out all forms of

terrorism", Prime Minister Shehbaz Sharif said in a statement.

"The provincial government has ordered an investigation and

a case has been registered against unknown assailants under the

terrorism law," a government official said, speaking on

condition of anonymity.

Pakistan has seen a resurgence in Islamist militancy since

2022, when a ceasefire between the Pakistani Taliban and the

government broke down.

Two Chinese nationals working for a power plant were killed

this week in a blast in the southern city of Karachi, for which

the Baloch Liberation Army (BLA), one of several insurgent

groups battling the government, claimed responsibility.

The BLA was also behind Balochistan's most widespread

violence in years in August, which targeted police stations,

railway lines, and highways, killing more than 70 people.

Armed men who stormed the residence of labourers from the

eastern province of Punjab last month killed seven.

On Friday, cross-fire between police and attackers killed

two suspected militants involved in a 2021 attack on dam project

workers that killed 13, including nine Chinese nationals.