Iran is preparing to bury slain Supreme Leader Ayatollah Ali Khamenei as the procession carrying his body approached the Shrine of Imam Reza, Iran's holiest shrine.

Khamenei will be buried at the shrine, located in his hometown of Mashhad.

The roads of Mashhad were thronged with mourners clad in black as thousands turned up to pay homage to the slain supreme leader.

Khamenei was killed on February 28, the day the war in West Asia broke out.

The funeral follows week-long public ceremonies that began on July 4. Iran's current supreme leader and Khamenei's son Mojtaba Khamenei remains absent from the ceremonies.

The week-long funeral ceremonies have been marred by renewed crossfire between US and Iran that has put the fate of the interim ceasefire agreement signed by the two nations in limbo.