LONDON—Boeing Co. Tuesday said it had signed a tentative agreement to sell jetliners to Iran, in what would be one of the Islamic republic’s biggest deals with a U.S. manufacturer since trade sanctions on Tehran were eased.

The proposed deal comes after months of talks between Boeing BA, -3.81% and Iran Air about a deal. Details of the potential transaction haven’t been disclosed by Boeing, although Iranian Transport Minister Abbas Akhoundi​ told state television​Tuesday​ that the deal could have a value of up to $25 billion, according to the Associated Press.