At least seven teachers were killed in a shooting at a school in northwestern Pakistan on Thursday in what appeared to be retaliation for an attack shortly before in which another teacher was shot dead, officials said.

Both incidents occurred in the Parachinar area of Kurram tribal district near the border with Afghanistan, they said.

Contradictory accounts were given by regional authorities about the motive for the killings.

A statement from the provincial chief minister’s office said it involved a property dispute, but the regional commissioner said sectarian antagonism appeared to be the cause.

The teacher killed in the first incident was a Sunni Muslim while those shot in the second attack at the school were Shi’ite Muslims, the commissioner, Saiful Islam, told Reuters.

“It is not clear whether the second incident was a reaction to the first one,” he said, adding security has been heightened in an area already tense due to sectarian violence.

The tribal district has a majority Shi’ite population who are often attacked by Sunni militant groups from the local Taliban movement. Sunni militants regard Shi’ites as heretics.

Local police said they were gathering more information as they investigated the incidents.