Footage showed Khamenei’s coffin, bearing the colours of the Islamic Republic, being carried aloft at the Grand Mosalla on Friday.
Iran’s President Masoud Pezeshkian was among those paying their respects after the coffin was placed at the vast religious complex.
Pakistan’s Prime Minister Shehbaz Sharif, whose country has mediated peace talks between the US and Iran, former Russian president Dmitry Medvedev and the Afghan Taliban’s Foreign Minister Amir Khan Muttaqi were in attendance.
Representatives from Iraq, Armenia, Turkey and several Gulf states – Saudi Arabia, Qatar and Oman among them, have also arrived for the processions.
There will be an official funeral ceremony in Tehran on Saturday, which the Tehran-based Mohammad Rasulullah Corps is leading, as part of six days of ceremonies.
Khamenei’s body will lie in the Grand Mosalla for three days, alongside the remains of family members who were also killed in the US and Israeli strikes in February.
Mohammad Rasulullah Corps commander Hassan Hassanzadeh said Khamenei’s coffin would be displayed on an elevated platform, with crowd flows designed to allow visitors to enter and leave within 15 to 20 minutes.
The supreme leader was killed during joint Israeli and US strikes on Iran in late February, precipitating a major regional war in the following months.
Speaking on Friday night in the US, President Donald Trump acknowledged the week of mourning taking place in Iran, adding that the country was “dying to settle” as negotiations to end the war continue.
“We gave them [Iran] a week off for a funeral because we’re nice,” he told a crowd gathered at Mount Rushmore for his address on the eve of 4 July celebrations marking the 250th anniversary of US independence.
