A group of 33 Saudi pilgrims, including 19 children and 14 adults, were hospitalized in Imam Reza Hospital in Mashhad with poisoning symptoms on Sunday, Abdollah Bahrami, the head of the hospital said.

Four children lost their lives despite extensive treatment by the Iranian medical staff.

The reason behind the poising of the pilgrims has not been determined yet.

Speaking to the Tasnim News Agency, Mashhad Prosecutor Gholam Ali Sadeqi said an investigation into different aspects of the case is underway.

He said a special inspector has been designated for the investigation, adding that so far, there has been no evidence suggesting that the incident was a deliberate act.

The Saudi pilgrims were staying at a hotel in the holy city of Mashhad in Khorassan-e Razavi province which houses the shrine of Imam Reza, the eighth Imam of Shiite Muslims.

Every year, the holy shrine of Imam Reza (AS) in Mashhad attracts nearly 30 million pilgrims from Iran and other countries.