"As we commemorate the late leader of the Islamic Republic of Iran Ayatollah Ali Khamenei, we hope that his honourable successor will find success and guidance in serving the great Iranian people, repelling absolute evil and preserving national unity and harmony," Sistani said.

Mojtaba Khamenei, 56, was named Iran's supreme leader on Sunday to replace his father Ali who was killed in an air strike at the start of the US-Israeli war against the Islamic republic on February 28.

But he has yet to appear in public after being wounded in the strike that killed his father and wife, according to officials.

Last week, Sistani, himself born in Iran, denounced an "unjust war" on the Islamic republic.

Despite his non-Iraqi roots, Sistani has been a vital figure in Iraq's recent history, guiding his followers through decades of dictatorship, occupation and conflict.

But his influence extends beyond Iraq with millions of followers across the Muslim world.

Sistani, who has lived in the Iraqi holy city of Najaf for decades, always had a complex relationship with his birthplace Iran and was known for resisting Tehran's growing influence in Iraq.

While Iran is ruled by clerics, Sistani has always avoided any formal role in government.