| QUETTA, Pakistan
QUETTA, Pakistan Separatist militants in Pakistan's Baluchistan province have claimed responsibility for killing six coal-mine workers as violence intensified in the resource-rich province.
Nuclear-armed Pakistan is already grappling with intensifying Islamist militant violence while struggling to revive a flagging economy.
A surge of separatist violence in Baluchistan will compound fears for the U.S. ally's stability.
Bullet-ridden bodies of six coal-mine workers were found in mountains near Marwar, 35 km (20 miles) east of the provincial capital, Quetta, on Saturday, a senior police officer said.
"Their hands and feet were bound with rope and they were shot in the head," police officer Wazir Khan Nasir told Reuters on Sunday.
The six, none of whom was from Baluchistan, were abducted outside their company offices in Marwar on Friday.
Baluch nationalists have for decades campaigned for greater autonomy and control of the province's abundant natural gas and mineral resources, which they say are unfairly exploited to the benefit of other parts of the country.
Baluch militants have also waged a low-level insurgency, at times targeting gas and mining infrastructure as well as "outsiders" from other parts of Pakistan.
A spokesman for the Baluchistan Liberation Army militant group telephoned a press club in Quetta on Saturday to claim responsibility for killing the six workers, saying it was in retaliation for the killing and kidnapping of Baluch people.
"If the military keeps on killing and abducting our people, such things will continue," said the spokesman, Meerak Baluch, according to a journalist who spoke to him.
Tension has surged in the province of bleak deserts and mountains since Thursday, when three Baluch political leaders were found shot dead.
Several people were killed in rioting that broke out in Quetta and other towns after the discovery of the three, who were abducted by unknown men days earlier.
Their supporters said they were taken away by security men.
The provincial government said the killing of the three was an act of terrorism and ordered an inquiry. The military blamed an "anti-state element" bent on undermining reconciliation.
The United States condemned the killing of the three men, saying one of them had recently helped in the release of a kidnapped American U.N. official. The United Nations expressed its serious concern and called for an immediate investigation.
Rights group Amnesty International also urged authorities to investigate the killing of the three, adding the government had failed to investigate an estimated 800 enforced disappearances in Baluchistan over the past two years.
Baluchistan borders Afghanistan and Iran and is Pakistan's biggest province in terms of area, but its population is the smallest and poorest.
Taliban Islamist militants fighting in Afghanistan also operate out of Baluchistan but have no links with the largely secular nationalists.
There have been were no reports of disruptions at gas fields over recent days.
(Writing by Kamran Haider; Editing by Robert Birsel and Jerry Norton)