Boeing said Saturday it had moved a step closer to completing a contentious jetliner sale to an Iranian airline, though the U.S. government still needs to give the green light before planes could be delivered.

Boeing said it had signed a final purchase agreement with Iran Aseman Airlines for up to 60 737 Max single-aisle planes, its newest model. The two parties earlier this year announced a memorandum of agreement for the transaction that could be valued at up to $6 billion at list price, though buyers typically get discounts.