The apparent crash of a helicopter carrying Iran's president and foreign minister has sent shockwaves around the region.
Details remained scant in the hours after the incident, and it was unclear if Iranian President Ebrahim Raisi and the other officials had survived.
Here's what we know so far.
Who was on board the helicopter?
The helicopter was carrying Iranian President Ebrahim Raisi, the country's Foreign Minister Hossein Amirabdollahian, the governor of Iran's East Azerbaijan province and other officials and bodyguards, according to the state-run IRNA news agency.
Raisi was returning from a trip to Iran's border with Azerbaijan earlier Sunday to inaugurate a dam with Azerbaijan's President Ilham Aliyev, the news agency said.
Where and how did the helicopter go down?
The helicopter apparently crashed or made an emergency landing in the Dizmar forest between the cities of Varzaqan and Jolfa in Iran's East Azerbaijan province, near its border with Azerbaijan, under circumstances that remain unclear.
Initially, Interior Minister Ahmad Vahidi said the helicopter "was forced to make a hard landing due to the bad weather and fog."
What is the status of the search?
Iranian officials have said the mountainous, forested terrain and heavy fog impeded search-and-rescue operations.
The president of the Iranian Red Crescent Society, Pir-Hossein Koulivand, said 40 search teams were on the ground in the area despite "challenging weather conditions."
The search is being done by teams on the ground, as "the weather conditions have made it impossible to conduct aerial searches" via drones, Koulivand said, according to IRNA.
If Raisi died in the crash, how might this impact Iran?
Raisi is seen as a protégé to Iran's supreme leader Ayatollah Ali Khamenei and a potential successor for his position within the country's Shiite theocracy.
Under the Iranian constitution, if he died, the country's first vice president, Mohammad Mokhber, would become president. Khamenei has publicly assured Iranians that there would be "no disruption to the operations of the country" as a result of the crash.
What has the international reaction been?
Countries including Russia, Iraq and Qatar have made formal statements of concern about Raisi's fate and offered to assist in the search operations.
Azerbaijani President Aliyev said he was "deeply concerned" to hear of the incident, and affirmed that Azerbaijan was ready to provide any support necessary. Relations between the two countries have been chilly due to Azerbaijan's diplomatic relations with Israel, Iran's regional arch-enemy.
Saudi Arabia, which is traditionally a rival of Iran although the two countries have recently made a rapprochement, also expressed concern in a statement and said it "stands by Iran in these difficult circumstances."
There was no immediate official reaction from Israel. Last month, following an Israeli strike on an Iranian consular building in Damascus that killed two Iranian generals, Tehran launched hundreds of missiles and drones at Israel. They were mostly shot down and tensions have apparently since subsided.
