Iran's news agency IRNA said a Boeing official and Iran Air's head Farhad Parvaresh signed the deal worth 15.7 billion euros ($16.6 billion) in Tehran on Sunday.

Most of Iran's fleet of 250 commercial planes pre-dates the Islamic Revolution, with scores of aircraft grounded because of a lack of spare parts, and its airlines overshadowed by a poor safety record.

Iranian Transport Minister Abbas Akhoundi said the modernization was an "important step." Parvaresh said the Boeings would help restore Iran's past role as a regional hub.

The first of the 50 737s and 30 long-haul 777s would be delivered in April, said Parvaresh. Signing for Boeing had been Fletcher Barkdull, a regional director (pictured above, right, with Parvaresh), IRNA reported.

Deal with Airbus also pending

Iran is also reported to be close to ordering 100 planes from Airbus, Europe's aviation giant, which also requires US Treasury approval because some of its parts are made in the United States.

Washington granted permission to Boeing and Airbus to sell planes to Iranian carriers in September - before the US presidential election. A historic agreement limiting the scope of Iran's nuclear program in exchange for the lifting of sanctions was made by Iranian and Western diplomats was reached in 2015.

Since the US election, however, Congressional Republicans have criticized the nuclear accord that included Iran, the United States, Britain, France, Germany, Russia and China and saw crippling sanctions lifted in exchange for Iran curbing its nuclear activities.

"We hope that despite changes in the US administration, the country will remain loyal to its commitments," said Akhoundi.

During his US election campaign, President-elect Donald Trump vowed to tear up the accord.

The Flight Safety Foundation said Iran's lack of new planes and spare parts had resulted in close to 1,700 people dying in civilian and military air disasters since 1979.

ipj/sms (AFP, Reuters, AP)