A major Iranian airline suspended flights to neighboring countries, adding to the country’s isolation caused by sweeping U.S. sanctions and a naval blockade that have sought to cut off Iran from the global economy.

Mahan Air, Iran’s most prominent commercial carrier, announced the measures on Wednesday, just over a week after the U.S. Treasury Department put restrictions on Iran’s aviation industry intended to severely limit its ability to operate abroad. The new U.S. measures also make it difficult for other countries and non-Iranian companies to work with the Iranian aviation industry, as doing so could be put them at risk of being punished by the U.S. government.

The flight suspensions are likely to further strain many Iranians’ already fraying links with the outside world and add to their hardship, with much of the population feeling squeezed by an American economic pressure campaign.

Mahan Air will stop flying to Oman starting on Thursday and to Turkey starting on Monday, it said in a notification sent to Iranian travel agencies on Wednesday. It did not explain why in detail, saying only that it would stop flights after unspecified decisions by the Turkish and Omani aviation authorities. It did not cite the sanctions.

The suspension of flights comes as a longstanding economic crisis in Iran has been made worse by the war. The U.S. Navy has instituted a blockade of Iran’s southern ports that has curtailed its ability to export oil or import key goods. The Iranian government raised some fuel prices this month because of the financial pressure, increasing the price at the pump for Iranians who were already enduring spiraling inflation and high unemployment.

Last month, the U.S. Treasury announced an “Economic D-Day” that threatened to punish countries and entities that did business with Iran. It said it would target Iran’s trade in gold and cryptocurrency, among other sectors, helping to send the price of Iran’s currency, the rial, to new lows and making imports more expensive.