Ayatollah Abbasali Soleimani died in hospital after being shot at a bank in Babolsar, in Mazandaran province.

Irna news agency said the attacker was arrested and the motive was not clear.

Ayatollah Soleimani was one of 88 clerics on the Assembly of Experts, which appoints the Supreme Leader and can theoretically remove him.

He also previously served as the personal representative of the current Supreme Leader, Ayatollah Ali Khamenei, in the restive south-eastern province of Sistan-Baluchistan, stepping down in 2019 after 17 years in the role.

Ayatollah Soleimani, who was in his mid-70s, was reportedly sitting inside a branch of Bank Melli in Babolsar on Wednesday morning when he was shot.

Hawzahnews, the official website of Iran's Shia seminaries, cited a witness as saying that a man grabbed a bank guard's gun and opened fire.

But the governor of Mazandaran, Mahmoud Hosseinipour, told state TV that the attacker was a bank guard, according to AFP news agency.

"So far, our information and documents indicate that this was not a security or terrorist act," it quoted him as saying.

Last April, two clerics were killed and a third was injured in a knife attack at a shrine in the the north-eastern city of Mashhad.

An Uzbek man was hanged in June after being found guilty of the stabbings, for which police did not reveal the motive.