Thousands of protesters shouting anti-military slogans displayed the bodies of 15 villagers in north-western Pakistan, claiming they were shot dead in their homes by security forces in an overnight raid.
Hours later, police dispersed the protesters using water cannons and tear gas.
The outcry came as thousands of supporters of a fiery Muslim cleric continued their anti-government protest for a third day in Islamabad, paralysing key areas of the capital.
The interior minister warned that the government could take "targeted action" if the demonstrators did not leave the city by today, but later backed off the threat after he was contradicted by the president.
Wednesday's display of the 15 bodies, which were wrapped in blankets, recalled a protest last week in the south-western city of Quetta. There, the relatives of dozens of Shiite Muslims killed in a bomb attack refused to bury the victims for four days until the government met their demand to dissolve the government of surrounding Baluchistan province.
Islamic custom dictates the dead should be buried as soon possible.
The villagers in the latest incident were killed late on Tuesday in an area known as Khyber Agency, part of the tribal region where the Pakistani military has been waging a campaign against Islamic militants.
An official with the Frontier Constabulary, which operates in the area, blamed militants for killing the villagers. There have been previous attacks by militants disguised in military uniforms, although such incidents are not common.
About 3,000 people gathered outside the house of the governor of north-west Khyber Pakhtunkhwa province in Peshawar. They said gunmen wearing military uniforms stormed homes and shot the villagers.
The protesters called on the military to end its operations in the Bara area where the shooting occurred. One sign written in Urdu read: "We are also Pakistanis. Don't kill us."