A former employee of Iran’s charitable Mostazafan Foundation killed three of his former coworkers on Wednesday before killing himself in a hostage taking in the western Iranian city of Ilam.

According to local police, seven other people were injured in the incident, some of whom are in critical conditions. One of them succumbed to his injuries at the hospital.

Fars news agency said that following a verbal argument with the employees of the Property and Real Estate Department of the Mostazafan Foundation of Islamic Revolution, the former employee took a gun from his car, and held several of his colleagues at gunpoint before he started a shooting spree on the premises.

According to unconfirmed reports, the hostage taker threw a grenade inside one of the rooms of the office.

No details about the identity or motive of the hostage taker were released, and local police authorities say the incident is under investigation.

Bonyad-e Mostazafan in the Islamic Republic’s second-largest commercial enterprise that is behind the state-owned National Iranian Oil Company. It is reportedly the biggest holding company in the Middle East.

The bonyad is associated with the Islamic Revolutionary Guard Corps where some of its head officials have come from.