One of Iran’s most important airlines has suspended flights on several international routes in a sign of the mounting struggles facing the country’s aviation industry after the US tightened sanctions on entities trading with Tehran. Mahan Air, among the country’s largest and most popular carriers, told travel agencies it was suspending flights to and from Istanbul and Ankara starting on Monday. Flights between Tehran and Muscat in Oman were suspended on Thursday.

In the notices to agencies seen by the FT, the airline did not specify the reason for the cancellations beyond saying the move had been made following decisions by aviation authorities in Turkey and Oman. It comes just over a week after the US Treasury announced that it was sanctioning 36 targets for “supporting Iran’s aviation sector”, which it accused of helping move weapons and personnel for the regime. While Mahan was already under sanctions, the latest round targeted several ground service providers and sales agents based in Turkey and elsewhere that the US said worked with the airline.

Treasury secretary Scott Bessent, who also announced sanctions on 27 other carriers as part of the package, threatened further penalties on any individual or company that continued to work with Iranian airlines. The sanctions are part of US President Donald Trump’s strategy to use economic pressure to force Iran to capitulate in its stand-off with Washington over the Strait of Hormuz. Foreign carriers have not returned to Iran since the US and Israel launched the war in February, and the latest suspension leaves Iranians with increasingly limited options to travel overseas.

About a third of the flights into Iran on Wednesday were cancelled or simply did not fly. About 50 of the expected 143 services did not operate, including more than half the planned flights from airlines Kish and Iran Airtour, according to data group Cirium. Turkey and Oman are important business hubs for Iranians, and travel agents in Tehran have warned clients that yet more flights could be cancelled.