A helicopter carrying President Ebrahim Raisi has had to make a "hard landing" after it got in difficulties, state media reports.
The details of what happened remain unclear, but here's a look at what we know so far:
According to local media, Raisi was heading to the city of Tabriz, in the north west of Iran, after returning from the border with Azerbaijan, where he opened the Qiz Qalasi and Khodaafarin dams
The helicopter was one of three travelling in a convoy
Iran's interior minister says rescuers are still trying to reach the site, but their efforts are being hampered by poor weather conditions
A reporter with Fars news agency says visibility in the mountainous and wooded area was down to only about five meters. The area is about 50km to the north of Tabriz
Ahmad Alirezabeigi, an Iranian MP for the city of Tabriz, says that emergency rescue workers have yet to find the location of the helicopter carrying the president
He says two other two helicopters in the convoy landed safely.
Who is Ebrahim Raisi?
Raisi, 63, was elected president on his second attempt in 2021. He is seen as a hardline cleric and regarded as a potential successor one day to Ayatollah Khamenei, the country's supreme leader since 1989.
In 2019, the Supreme Leader named him to the powerful position of head of the judiciary.
Raisi was also elected as deputy chairman of the Assembly of Experts, the 88-member clerical body responsible for electing the next Supreme Leader.
Rescuers have yet to make contact with the helicopter convoy
Bad weather - with heavy fog and rain - is hampering the efforts of rescue teams to get to the accident site in the mountains in the north west of Iran.
The condition of those on board the helicopter remains unknown for now, with reports that no contact has yet been made.
President Raisi was travelling with the Iranian foreign minister in a convoy of three helicopters over the area - two of the helicopters are reported to have landed safely.
Raisi was elected president on his second attempt in 2021.
He is seen as a hardliner and regarded as a potential successor one day to Ayatollah Khamenei as Supreme Leader.
State media urges Iranians to pray for Raisi
Iran's semi-official Fars news agency has called on Iranians to pray for President Ebrahim Raisi, following reports a helicopter in a convoy he was travelling in has been involved in an accident.
Footage has also emerged on state television showing worshippers praying for the president’s health in the city of Mashhad.
It will take time to find helicopter location - the interior minister
We can bring you more comments now from Iran's Interior Minister Ahmad Vahidi, who says "various rescue teams" are still searching for the helicopter.
Speaking to Iranian state television, Vahidi says that it will take "time to get to the location" of the crash site because of the "bad weather conditions and fog in the area".
"Things are under control and rescue teams are doing their work. We hope it will be done as soon as possible," he adds.
Raisi attended dam openings before helicopter accident
As we've been reporting, Iran's President Ebrahim Raisi was heading to the north-eastern city of Tabriz after returning from an Iran-Azerbaijan border area when the incident occurred.
Raisi had been visiting the Iran-Azerbaijan border, where he opened the Qiz Qalasi and Khodaafarin dams with his Azeri counterpart Ilham Aliyev.
Here are some of the latest images we've received of his visit earlier today.
Who is Hossein Amir-Abdollahian?
Iran’s top diplomat Hossein Amir-Abdollahian is also in focus in this fateful moment.
In the past several months, as urgent diplomacy intensified around the Israel-Gaza war, he has been the voice on the phone, the face at the meeting, in constant contact with Iran’s allies, but also Arab and Western foreign ministers.
He occupies a key post in a system where ultimate power lies with the supreme leader, and where the Islamic Revolutionary Guards Corps (IRGC) hold sway over foreign policy.
During his decades in senior positions in the foreign ministry, he was known to have developed close ties with the IRGC, including its former commander Qasem Soleimani.
Since Ebrahim Raisi assumed the presidency in 2021, Abdollahian has been the Islamic Republic’s frequent flyer, travelling to capitals around the world in efforts to push back against efforts to isolate Iran, and to find ways to ease the impact of crippling international sanctions.
Three rescue workers missing, Red Crescent says
Three rescue workers searching for the crashed helicopter have gone missing, a Red Crescent spokesperson says.
The search teams are close to the where the helicopter may have crashed, the spokesperson adds.
They say that the search operation will slow down as as the weather is expected to get "severely cold" soon, with more rain on the way.
Azerbaijan 'profoundly troubled' over helicopter crash reports
Azerbaijan's President Ilham Aliyev says he was "profoundly troubled" after hearing reports about a helicopter crash involving Ebrahim Raisi.
Aliyev was with the Iranian president earlier today to open two dams around the Iran-Azerbaijan border.
"Today, after bidding a friendly farewell to the President of the Islamic Republic of Iran, Ebrahim Raisi, we were profoundly troubled by the news of a helicopter carrying the top delegation crash-landing in Iran," he writes on X.
"Our prayers to Allah Almighty are with President Ebrahim Raisi and the accompanying delegation".
He adds that Azerbaijan is ready to offer any assistance needed.
Red Crescent denies reports of missing rescue workers
Earlier, a spokesperson for the Red Crescent said three of the group's rescue workers had gone missing during the search for the crashed helicopter.
The organisation has now said that none of its workers are missing.
"All official updates about rescue operation will either come from the task force in charge of these operations," a spokeswoman added.