Saudi Arabia has summoned Iran's ambassador over a mass poisoning which killed four children and left 28 other Saudi pilgrims sick, official media said on Tuesday.

Riyadh called in the envoy "to express its serious concern over the incident, hoping the Iranian authorities quickly carry out investigation procedures to uncover the circumstances", said Osama Nugali, the foreign ministry's information division chief, quoted by the Saudi Press Agency.

The website of Iran's Press TV reported that the poisoning occurred in Mashhad city, the spiritual capital of the Shiite country.

It quoted Abdollah Bahrami, head of Imam Reza Hospital in Mashhad, as saying as many as 33 Saudi pilgrims were hospitalised on Sunday with poisoning symptoms. Four children had died.

They had been staying at a hotel in the holy city, Press TV added.

It cited Mashhad prosecutor Gholam Ali Sadeqi as saying a probe has been launched but there was no initial evidence of foul play.

The poisoning came with tensions high between Sunni-dominated Saudi Arabia and its regional rival Iran.

Saudi Arabia leads an Arab-dominated coalition which for more than two months has been bombing Iran-backed Shiite rebels in Yemen.

The kingdom's Shiite minority has also been grieving over the murder of 25 people blown up in two separate suicide bombings at mosques in eastern Saudi Arabia last month.

Both attacks were claimed by the Islamic State jihadist group, a Sunni extremist organisation that considers Shiites to be heretics.