Sectarian fighting in northwestern Pakistan which killed more than 80 people last week restarted on Monday, officials said, breaching a seven-day brokered ceasefire.
Pakistan is a Sunni-majority country, but Kurram -- in Khyber Pakhtunkhwa province, near the border with Afghanistan -- has a large Shia population and the communities have clashed for decades.
An uptick in violence began last Thursday when two separate convoys of Shia Muslims travelling under police escort were ambushed, sparking two days of gun battles.
At least 82 people were killed and 156 more wounded before the regional government brokered the ceasefire on Sunday night.
But late Monday Kurram deputy commissioner Javedullah Mehsud told AFP, "reports of tribal clashes and gunfire continue to emerge from several areas".
A security official stationed in Kurram who asked not to be named confirmed "clashes are ongoing" in at least three areas but said that no fresh casualties had yet been reported.
"There are significant disagreements over the exchange of prisoners and bodies," he said. "According to my information, both communities are currently holding over 18 individuals hostage, including eight women."
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 short-lived truce was brokered by a delegation from the provincial capital of Peshawar, but even their helicopter came under fire when it arrived in the region at the weekend, one security official said.
The feuding is generally rekindled by disputes over land in the rugged mountainous region, and fuelled by underlying tensions between the communities.