A helicopter carrying President Ebrahim Raisi of Iran and his foreign minister crashed on Sunday in the country's mountainous northwest, according to state media, deepening the turmoil that has gripped the nation on both the international and domestic fronts in recent months.

Mr. Raisi, 63, was traveling from Iran's border with Azerbaijan to inaugurate a joint dam project.

The helicopter, carrying Mr. Raisi and Foreign Minister Hossein Amir Abdollahian, state media reported, crashed near the city of Varzaghan around 1 p.m. local time, in bad weather and thick fog.

Search and rescue teams scoured an area of tall mountains and dense forest through rain and fog for more than 10 hours.

At one point the authorities called off the aerial search because of the weather, dispatching on foot soldiers, elite commandos of the Revolutionary Guards and 40 rescue teams to locate the crash site.

Even well into the night, state media had not yet reported on casualties, or on the condition of the president or anyone else aboard.

The cause of the crash was also unknown.

"There will be no disruption in the country's operation," Supreme Leader Ayatollah Ali Khamenei said in an address on state TV.

"Senior officials are doing their work and I have advised them on the necessary points and all of the country's operation will carry on smoothly and orderly." Mr. Raisi, a conservative who violently crushed dissent, is widely viewed as a possible successor to the supreme leader.

The uncertainty over his fate comes during a particularly tumultuous period for Iran.