WASHINGTON, May 21 (Reuters) - The United States on Thursday imposed sanctions on two firms based in Iraq and in the United Arab Emirates for helping Iran purchase second-hand civilian aircraft.

The U.S. Treasury said the sanctions applied to Iraq-based Al-Naser Airlines as well as UAE-based Sky Blue Bird Aviation for providing support to Iranian airline Mahan Air.

The sanctions came after a senior Israeli official took a swipe at the United States over Iran's purchase of used commercial planes in the past three months, which he said took place even after Israeli intelligence flagged the pending sales to the Obama administration.

A long-standing ban on the export of aircraft spare parts to Iran was eased under an interim nuclear deal between Tehran and world powers in late 2013 but the sanctions regime continues to restrict sales of planes.

(Reporting by Jason Lange; Editing by Bill Trott) ((jason.lange@thomsonreuters.com; 202 310 5487; Twitter @langejason; Reuters Messaging: jason.lange.thomsonreuters.com@reuters.net))

Keywords: IRAN NUCLEAR/SANCTIONS