Funeral ceremonies will begin today for the late Iranian President Ebrahim Raisi after his death in a helicopter crash, as authorities investigate what caused the crash on a remote mountainside during foggy weather on Sunday morning.

Raisi’s death, alongside the foreign minister and other officials, has left the Islamic Republic’s hardline establishment facing an uncertain future as it navigates rising regional tensions — including Israel’s war against its ally Hamas — and domestic discontent.

Iran’s government has arranged multiple days of mourning culminating in a funeral this week for the 63-year-old ultraconservative cleric who had once been seen as a potential successor to current Supreme Leader Ayatollah Khamenei.

Tuesday will begin with funeral prayers and a procession in the city of Tabriz, the largest city in the northwestern region of Iran where the chopper crashed, according to Mohsen Mansouri, the head of the funeral planning committee and Iran’s vice president of executive affairs.

Later that day, the bodies of the victims will be transferred to the holy Shiite city of Qom, where many of the clerics who make up Iran’s theocratic elite are trained, before then heading to the capital Tehran.

Large ceremonies are planned in Tehran’s Grand Mosallah Mosque on Wednesday. Mansouri announced a public holiday and the closure of offices all over the country that day so that processions could take place.

Raisi’s body will then be moved to the historic Imam Reza shrine in Mashhad where Ayatollah Khamenei will conduct prayers, according to Mehr News.

There is no indication of what might have caused the crash – and why so many senior Iranian government officials were traveling in a single, decades-old helicopter.