One of the three-helicopter convoy of Iran's President Ebrahim Raisi was involved in "an accident" on Sunday and the duo has remained missing since then, state media reported.

An Iranian official told Reuters that the lives of Raisi and Foreign Minister Hossein Amirabdollahian were "at risk following the helicopter crash", which happened along a mountain terrain amid heavy fog.

The president was on his way back from a visit to Iran's neighbour Azerbaijan.

"We are still hopeful but information coming from the crash site is very concerning," said the official, speaking on condition of anonymity.

"The harsh weather conditions and heavy fog have made it difficult for the rescue teams to reach the accident site," AFP earlier reported quoting state TV.

According to some local media, Foreign Minister Hossein Amir-Abdollahian and local officials were travelling in the same helicopter as Raisi.

Raisi was visiting East Azerbaijan province on Sunday where he inaugurated a dam project in the company of his Azeri counterpart, Ilham Aliev, on the border between the two countries.

Raisi, 63, has been president of the Islamic Republic since June 2021.