By Parisa Hafezi and Elwely Elwelly

DUBAI (Reuters) -A helicopter carrying Iranian President Ebrahim Raisi and his foreign minister crashed on Sunday as it was crossing mountain terrain in heavy fog, an Iranian official told Reuters, and rescuers were making their way to the site of the incident.

The official said the lives of Raisi and Foreign Minister Hossein Amirabdollahian were "at risk following the helicopter crash", which happened on the way back from a visit to Iran's border with Azerbaijan.

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

The bad weather was complicating rescue efforts, the state news agency IRNA reported. The chief of staff of Iran's army ordered all the resources of the army and the elite Revolutionary Guard to be put to use in the search and rescue operations.

State TV stopped all its regular programming to show prayers being held for Raisi across the country and, in a corner of the screen, live coverage of rescue teams deployed on foot in the mountainous area in heavy fog.

The rescue teams were expected to reach the site of the crash later on Sunday evening, state TV reported.

Raisi, 63, was elected president in 2021, and since taking office has ordered a tightening of morality laws, overseen a bloody crackdown on anti-government protests and pushed hard in nuclear talks with world powers.

In Iran's dual political system, split between the clerical establishment and the government, it is the supreme leader rather than the president who has the final say on all major policies.

But many have seen Raisi as a strong contender to succeed his 85-year-old mentor, Supreme Leader Ayatollah Ali Khamenei, who has strongly endorsed Raisi's main policies.

Raisi's victory in a closely managed election in 2021 brought all branches of power under the control of hardliners, after eight years when the presidency had been held by pragmatist Hassan Rouhani, who negotiated a nuclear deal with Washington.

However, Raisi's standing may have been dented by widespread protests against clerical rule and a failure to turn around Iran's economy, hamstrung by Western sanctions.

Raisi had been at the Azerbaijani border to inaugurate the Qiz-Qalaisi Dam, a joint project.

Interior Minister Ahmed Vahidi told state TV only that one of the helicopters in a group of three had come down in the incident, and that authorities were awaiting further details.