With heavy weapons including mortar shells, the violence hit Kurram district near the border with Afghanistan where the same tribes fought in July.

“The conflict, initially over land, involves two tribes which has turned the dispute into a sectarian clash,” a senior administrative official stationed in Kurram told AFP on condition of anonymity.

He said 15 people had been killed since Saturday.

The Associated Press of Pakistan reported around twenty other people had been wounded.

The Kurram district, formerly a semi-autonomous area, has a history of bloody clashes between tribes belonging to the Sunni and Shiite sects of Islam that have claimed hundreds of lives over the years.

The last clashes in July killed 35 people and ended only after a jirga (tribal council) called a ceasefire, with officials attempting to broker a new truce.

Tribal and family feuds are common in Pakistan.

However, they can be particularly protracted and violent in the mountainous northwestern region of Khyber Pakhtunkhwa, where communities abide by traditional tribal honour codes.