The Boeing Co.’s historic sale to Iran Air could be undone either by U.S. hawks who take a hardline on Iran or by Tehran’s own bad behavior.

The Islamic nation has used the airline to ferry weapons and fighters around the Middle East in support of groups deemed terrorists by the U.S. State Department. The Obama administration used a technicality to sidestep the issue while negotiating last year’s nuclear agreement.

If Iran Air flights are used for anything other than civil aviation, the U.S. could pull the license for Boeing’s sale, State Department spokesman John Kirby told the Associated Press.

Boeing’s sale — which is worth as much as $25 billion at list prices — has come under fire by hawks in Congress. Representatives Peter Roskam and Jeb Hensarling asked the company to reconsider the sale in a letter last week.

The aerospace giant “will continue to follow the lead of the U.S. Government,” Boeing’s top lobbyist, Tim Keating, replied in a letter sent Thursday.

If any current or future Boeing customer or supplier is blacklisted by the U.S., Boeing would immediately stop doing business with them, he said.

Kirby told reporters Thursday that the State Department “would or will turn a blind eye to Iran’s state sponsorship of terrorism or their terrorist-supporting activities.” But he would not explain why the U.S. took off sanctions on Iran Air.

In his letter, Keating said that the administration and Boeing have worked closely together for nearly two years during negotiations around the seven-nation agreement covering Iran’s nuclear program.

It has been “made clear to us in those consultations” that providing new Boeing and Airbus airplanes to Iran was “key and essential to reaching closure on the agreement,” the Boeing executive told the Congressmen.

Airbus and Iran Air signed a sales agreement worth about $27 billion at list prices.

Boeing’s deal is expected to be worth about the same amount. The company and Iran Air have signed a memorandum of agreement that the airline intends to buy 80 Boeing jetliners — reportedly including 777s — worth $17.6 billion at list prices and lease 29 new 737s.

Material from the Associated Press was used. Dan Catchpole: 425-339-3454; dcatchpole@heraldnet.com; Twitter: @dcatchpole.