A plane crashed into an Iranian mountain Sunday, and all 65 people on board were reportedly killed. While the government says the 25-year-old turboprop lost its way in thick clouds, some suspect that it malfunctioned — a chronic problem in a country with an air fleet that is decrepit after decades of international sanctions.

The Aseman Airlines ATR-72 took off from Tehran with 59 passengers, two pilots, two flight attendants and two security guards, the Associated Press reported. It was bound for Yasuj, a city 500 miles to the south.

But about 90 minutes into the flight, the AP wrote, the plane crashed into the Zagros Mountains amid fog and disappeared from the radar. Local residents heard the impact, according to Iranian news reports, but rescue helicopters couldn't reach the site because of the bad weather.

Searchers eventually had to travel to the mountain on foot, the BBC reported. “We learned that unfortunately ... our dear passengers had lost their lives,” an airline spokesman told the AP afterward.

Ayatollah Ali Khamenei, Iran's supreme leader, and President Hassan Rouhani offered their condolences.

The airline blamed the crash on the weather, and Al Jazeera confirmed that clouds had shrouded the mountain range. But this was only the latest in a string of deadly plane incidents in Iran, which has not properly maintained its air fleet as it has contended with international sanctions.

The most recent fatal crash was in 2011, the AP reported, when 77 died on board an Iran Air Boeing 727 caught in a snowstorm.

Aseman Airlines, which is partially owned by the government, has had crashes in 1994 and 2008. The airline has been banned in the European Union over safety concerns, the AP wrote.

The 1993 turboprop that went down Sunday had been grounded for seven years until October, when it was put back into service, Al Jazeera reported. It had malfunctioned at least once since its reactivation and made an emergency landing for repairs last month. After Sunday's crash, Al Jazeera wrote, Aseman Airlines deleted references on its social-media accounts to the plane's years-long grounding, fueling suspicion of a coverup.

An international agreement struck in 2015 under U.S. leadership raised hope that Iran could soon modernize its air fleet, as the country promised to limit its nuclear program if international sanctions were dropped. President Trump, however, has repeatedly threatened to scuttle the agreement since he took office last year, leaving its fate in doubt.

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