The United Nations has expressed "serious concern" over the killing of three ethnic Baloch leaders that has sparked a number of riots.
It urged an immediate investigation into the deaths of the three, who supporters say went missing after being detained by security forces.
An army spokesman has blamed "anti-state" elements for the killings.
Strikes have been called across the province. One policeman died in riots on Thursday and more trouble is feared.
There has been a long-waged insurgency by nationalists in Balochistan for a greater share of natural resources and more autonomy.
A statement by Michele Montas, spokeswoman for the UN secretary general, read: "The United Nations calls on the government of Pakistan to immediately investigate these murders and to ensure that the Balochistan Qaum Dost Committee continues its important work."
The victims were members of the committee that was recently formed by the government of Pakistan to investigate the case of missing persons in the province, most notably abducted UN worker John Solecki, who was freed last Saturday.
The three leaders killed were named as Ghullam Muhammad Baloch, Lala Munir Baloch and Sher Muhammad Bugti.
Prime Minister Yusuf Raza Gilani has condemned the killings, calling them an attempt to sabotage reconciliation efforts.
A lawyer and former opposition leader in the province, Kachkol Ali, said that the three were picked up by members of a security agency from his chambers in Turbat last Friday.
Their decomposed bodies were found late on Wednesday night near Turbat. Apparently they had been killed more than two days previously.
The BBC's M Ilyas Khan in Islamabad says the statement by the army spokesman is highly unusual. It terms the murders "regrettable" and blames "anti state elements... out to destabilise and undermine the reconciliatory efforts of the government".
The spokesman said it was "unfortunate and not in the interest of the country to make serious allegations against security agencies without knowing the facts and evidence".
Our correspondent says the army's internal intelligence wing, the Military Intelligence, is widely held responsible by many people in Balochistan for "disappearances" of political activists this century.
Many of them have been killed or maimed by torture.
It is feared protests and riots will continue across Balochistan on Friday and over the weekend.
Political groups have issued a general strike call for Friday and the weekend, shutting down all businesses and transport.
The government has already shut educational institutions in the province, while the lawyers are boycotting courts in protest.
Reports from Quetta suggest there is a shutdown across the city with very little traffic on the streets.
On Thursday a policeman was killed by protesters' gunfire in the town of Khuzdar.
In Quetta, three policemen were injured when a grenade was thrown at a police van.
A number of banks and offices were set on fire.
In August 2006, Balochistan experienced widespread rioting and strikes after the killing of tribal leader Nawab Akbar Bugti. Hundreds were arrested.
Writing recently on Balochistan, BBC columnist Ahmed Rashid pointed to the worsening situation in the province, where the wide-ranging political and economic grievances of the alienated Baloch people have remained largely forgotten and unaddressed.
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