The Treasury said Al-Naser Airlines, based in Iraq, was used as a "cutout" to procure eight Airbus A340 aircraft and one A320 for transfer early this month to Mahan Air, which was placed under sanctions in 2011 for providing transport services to Iran's Revolutionary Guards, or IRGC-QF, and the Lebanese militia Hezbollah.
Both groups have been designated by the US as terror and terrorist-supporting organizations.
Al-Naser obtained the nine aircraft "from unwitting European vendors," the Treasury said in a statement, without providing further identification.
The Treasury also blacklisted a Syrian businessman, Issam Shammout, and his company Sky Blue Bird Aviation, for helping Mahan Air obtain aircraft and parts. Shammout, it said, is chairman of Syria-based Cham Wings, also blacklisted by the Treasury since 2011.
The new sanctions forbid US companies and individuals from doing business with the blacklisted entities and individuals, and block their assets and interests in US jurisdictions.
"We will continue to actively counter Iranian sanctions evasion, whether in support of terrorist entities or other sanctioned parties," Treasury Acting Under Secretary for Terrorism and Financial Intelligence Adam Szubin said in the statement.
"We will not hesitate to sanction those who help in these endeavors."
Iran's aviation sector has faced difficulties obtaining aircraft and parts since an embargo dating from 1995 that prevented Western manufacturers from selling equipment and spare parts to Iranian companies.
Those restrictions were partially lifted by an interim agreement on Iran's nuclear program that came into force in January 2014.
This allowed for the sales of spare parts, though direct sales of planes remained banned.