An attacker has stabbed an Iranian cleric to death and wounded two others, one of them seriously, in Iran's shrine city of Mashhad.

The assailant struck on Tuesday as large crowds of worshippers gathered in the courtyard of the shrine of Imam Reza, of one of the most revered figures in Shia Islam, said the governor of Khorasan Razavi province, Yaghoub Ali Nazari.

"A man stabbed three Shia clerics with knives, killing one and wounding two others," said Nazari, adding that "one of the injured is in serious condition".

"Preliminary investigations show that the attacker committed this action under the influence of takfiri currents", he added.

The term "takfiri" is used to describe Muslims who take it upon themselves to brand others as apostates and thus condemn them to death, and usually refers to extremists groups.

The assailant and four suspected accomplices were arrested after the bloody attack in the Imam Reza shrine's courtyard on Tuesday, said Mohammad Hossein Doroudi, the chief prosecutor of the northeastern city.

"The attacker is a foreign national," he told the Fars News Agency, without specifying the country.

Identity of assailant under investigation

Mashhad, Iran's second city, attracts pilgrims from across the country during religious events, including the Muslim holy month of Ramadan, which began on Sunday in Iran.

Amateur video footage showed a man lying in a pool of blood in the courtyard of the site with golden domes and minarets.

The Astan Quds Razavi charitable foundation which runs the shrine said: "With the vigilance of the pilgrims and the efforts of security forces, the assailant was immediately arrested and handed over to the police, and the injured were quickly taken to the hospital."

"The identity of the assailant is under investigation," added the foundation, whose large asset portfolio was managed from 2016 to 2019 by Iran's President Ebrahim Raisi.

State news agency IRNA published mobile phone footage of the arrest of a presumed assailant in which several people were seen pushing a young man in the courtyard.

People were heard shouting "don't beat him up!" in the video, as some tried to prevent him from being attacked.

Iran has a population of 83 million, 90 percent of whom are Shia.

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