Iranian authorities are preparing for one of the largest public mourning events in the history of the Islamic Republic, as state-linked media report new details on the funeral plans for former supreme leader Ali Khamenei.

The main preparations are centered in Tehran, where authorities are preparing for massive crowds. Mohammad Amin Tavakolizadeh, Tehran’s deputy mayor for social and cultural affairs, said officials are preparing for “a crowd of more than 15 to 20 million people in the capital.” The central funeral ceremony is expected to last at least a full day.

The funeral ceremonies were originally expected to begin shortly after Khamenei’s death, with plans for several days of public mourning and farewell events in Tehran. However, Iranian authorities later postponed the ceremonies, saying they needed additional time to prepare for the unprecedented crowds expected to attend. Despite the extensive preparations now underway, Iranian authorities have still not released a final official schedule for all stages of the funeral. The public is expected to receive three official days of mourning to pay final respects.

After the events in Tehran, the funeral procession is expected to continue to Qom and Mashhad, two of Iran’s most important religious centers. The route would turn the funeral from a single ceremony into a national religious and political event across the Islamic Republic’s core cities.

Khamenei is expected to be buried near the Imam Reza shrine in Mashhad, one of the holiest sites in Shiite Islam. Iranian reports said the burial place reflects Khamenei’s will and the wishes of those close to him, as Tehran seeks to frame the funeral as both a farewell to the man who ruled Iran for decades and a show of regime continuity.