Sadr, a Muslim Shiite leader, has the ability to mobilise tens of thousands of his supporters with a single message and presents himself as an anti-corruption champion, often clashing with Iraq's political leadership.

He has repeatedly taken supporters and opponents by surprise with major announcements on social media, such as a Twitter message last year on his "definitive retirement" from politics.

In a statement shared on the cleric's official Twitter page on Friday, Sadr said he had decided to "freeze the movement... for at least a year".

The move would not affect religious activities including Friday prayers and an institution dedicated to his father's legacy, the statement said.

Sadr retains a devoted following of millions among the country's majority Shiite population, and claims direct lineage to Prophet Mohammed.

His rise was aided by the reputation of his father, Grand Ayatollah Mohammed Sadek Sadr, whom former dictator Saddam Hussein had assassinated in 1999.

The mausoleum in the city of Najaf where his father is buried would remain closed through the Muslim fasting month of Ramadan that ends later in April, according to Sadr's statement.

"That I may be a reformer for Iraq... but fail to reform the Sadrist movement, is a transgression," the cleric said.

"And it is a serious issue to continue leading the Sadrist movement as it includes... some corrupt elements" within it, he said.

Sadr was referring to a fringe group appearing in a video shared on social media and reported by Iraqi media, calling to "pledge allegiance to the awaited imam, Sayyed Moqtada Sadr".

Faithful believe the Mahdi, the twelfth imam of Shiite Islam, disappeared more than 1,000 years ago and will return one day to usher in a new era of peace and harmony.

In response to the video, authorities issued arrest warrants against "65 suspects from a gang that promotes ideas that incite dissent and disturb public security", a statement from the judiciary said.

In August, Sadr announced he was retiring from politics and closing institutions linked to his movement, in a statement that came amid political wrangling over the nomination of a prime minister and resulted in deadly clashes in Baghdad between his followers, the army and paramilitary forces.

Earlier last year he had ordered all 73 lawmakers affiliated with his movement to quit parliament in a show of force meant to break a logjam in political negotiations.