Pakistan is a Sunni-majority country, but Kurram -- in Khyber Pakhtunkhwa province, near the border with Afghanistan -- has a large Shiite population and the communities have clashed for decades.
"Both sides have agreed to a seven-day ceasefire, during which they will also exchange prisoners and return bodies to one another," said Muhammad Ali Saif, spokesperson for the Khyber Pakhtunkhwa provincial government.
A second local official told AFP that efforts were being made to return up to 20 people who were missing on both sides.
The latest violence began on Thursday when two separate convoys of Shiite Muslims travelling under police escort were ambushed, killing at least 43 and sparking two days of gun battles.
"The clashes and convoy attacks on November 21, 22, and 23 have resulted in 82 fatalities and 156 injuries," said a local administration official, speaking on condition of anonymity.
"Among the deceased 16 were Sunni, while 66 belonged to the Shia community," he told AFP.
Around 300 families fled on Saturday as gunfights with both light and heavy weapons continued into the night. No fresh casualties were reported on Sunday morning, however.
"The mobile network across Kurram remains suspended and traffic on the main highway is halted," said the local administration official.
Police have regularly struggled to control violence in Kurram, which was part of the semi-autonomous Federally Administered Tribal Areas until it was merged with Khyber Pakhtunkhwa in 2018.
The ceasefire deal came after a delegation from the provincial government held talks with the Shiite community on Saturday and met the Sunni community on Sunday.
A security official in the provincial capital of Peshawar told AFP the negotiators' helicopter had come under fire as it arrived in the region, although no one was harmed.
Once a truce was agreed, "we can begin addressing the underlying issues," provincial Law Minister Aftab Alam Afridi said earlier Sunday.
Last month at least 16 people, including three women and two children, were killed in a sectarian clash in Kurram.
Previous clashes in July and September killed dozens of people and ended only after a jirga, or tribal council, called a ceasefire.
The Human Rights Commission of Pakistan said 79 people were killed between July and October in sectarian clashes.
Several hundred people demonstrated against the violence on Friday in Pakistan's two largest cities, Karachi and Lahore.
