Washington: The US ramped up sanctions on Iran on Thursday, targeting several airlines it said were linked to the country's Islamic Revolutionary Guard Corps (IRGC).

The US Treasury placed on its blacklist nine individuals and entities in Iran and Turkey for obtaining aircraft parts, including restricted US-made parts, and supporting the operations of Mahan Air, Caspian Air, Meraj Air, and Pouya Air.

The nine were labelled "Specially Designated Global Terrorists" for their support of the four carriers, which are all already under US sanctions.

US Treasury Secretary Steven Mnuchin said that, by helping the four, "they extend a lifeline to the IRGC-QF and enable the Iranian regime to transport weapons, fighters, and money to its proxies, including Hezbollah, and to prop up the brutal Assad regime" in Syria.

"Countries and companies around the world should take note of the risks associated with granting landing rights and providing aviation services to the airlines used by Iran to export terrorism throughout the region."

The sanctions excluded Iran Air, the country's flag carrier with the largest fleet, and Aseman Airlines, which operated an ATR-72 aircraft which crashed into the mountains of southwestern Iran in early March, killing 66.