Riyadh (AFP) - Saudi Arabia's top cleric hit out at Iranian film "Muhammad" on Wednesday describing its portrayal of the prophet's childhood as a "hostile act" and a "distortion" of Islam.

Iran's most expensive movie, which opened nationwide in the Shiite Islamic republic last week, depicts the prophet on screen, an act that is prohibited in Sunni Islam.

"This is an obscene work... It is a distortion of Islam," Saudi Arabia's Grand Mufti Abdulaziz al-Sheikh told Al-Hayat newspaper. "It is a hostile act against Islam.

"This is a mockery of the prophet and a degradation of his status," he said.

Shiite Iran and Sunni Saudi Arabia, the birthplace of Islam and home to its two holiest sites, are regional rivals and frequently accuse each other of seeking to destabilise the Middle East.

The Mecca-based Muslim World League also condemned the movie, insisting that portraying the prophet is prohibited.

The league's secretary general Abdullah al-Turki urged Tehran to "suspend and prevent the screening of the movie" and called on Muslims to boycott it.

While Iran has denounced cartoons of the prophet like those published by French satirical magazine Charlie Hebdo, Shiites are generally more relaxed than Sunnis about depiction of religious figures.

Directed by Majid Majidi, the visually stunning 171-minute film cost around $40 million (36 million euros), partly funded by the state, and took more than seven years to complete.

Majidi says the aim of his work, the first part of a trilogy, is to reclaim the rightful image of Islam, which he said extremists have distorted.