A separatist politician whose mutilated body was found in Pakistan's restive southwest had helped secure the release of a kidnapped American U.N. worker, the U.S. Embassy said.
The remains of Ghulam Mohammed Baloch and two others were discovered in Baluchistan province on Thursday, six days after they were reportedly abducted by armed men.
Their deaths sparked rioting across the region, where ethnic Baluch groups have waged a long and often violent struggle for greater autonomy that apparently included the kidnapping of the American.
Baloch played "an active role" in seeking the release of John Solecki, the U.N. refugee agency staffer freed unharmed last weekend, the U.S. Embassy said.
The American government condemned the killings and urged Pakistani authorities to bring those responsible to justice, the embassy said in a statement late Thursday.
'Serious concern' about the killing
The U.N. also expressed "serious concern" about the killing.
Provincial officials have pledged a full investigation.
Rights groups accuse Pakistani security forces of abducting scores of Baluch activists and secretly holding them in a bid to crush the yearslong movement for greater control of natural resources in the impoverished region. Several leaders have been killed.
Gunmen abducted Solecki in the regional capital, Quetta, in February and threatened to kill him unless authorities freed hundreds of people allegedly held in Pakistani jails.
The government said it had "traced" some 200 missing persons, but it remains unclear if any were released to secure Solecki's freedom.
A U.N. statement said all three slain Baluch leaders were involved with a committee set up by the provincial government to investigate disappearances. It urged the government to ensure the committee continued its "important work."
Unrest could be further fueled
The killings risk fanning unrest in Baluchistan, another source of instability in a country already struggling to counter rising Islamist violence and serious economic problems.
On Friday, police said a roadside bomb wounded three civilians near Khuzdar, and that rioting students set fire to two banks in another southwestern town. One policeman was killed and several others injured during the violent protests Thursday, police said.
Critics say the security forces' focus on combating secular separatist groups reduces their ability to confront Taliban militants using Baluchistan as a base to attack Afghanistan.
This week, provincial government chief Nawab Mohammed Aslam Raisani denied the presence of al-Qaida or Taliban leaders in the region and said any expansion of U.S. missile attacks to Baluchistan would be unjustified.