In the shadow of the final weeks of nuclear talks, Iran and the United States appeared headed on Tuesday toward a possible confrontation over the recent purchase of nine used Airbus jetliners by Mahan Air, an Iranian airline blacklisted under American sanctions more than three years ago.

Mahan Air acquired the planes � eight A340s and one A321 � in May from sellers in Iraq, Syria and the United Arab Emirates as part of what was described as an expansion plan to service Mahan�s international routes.

The United States Treasury Department, which polices compliance with sanctions, said at the time not only that the purchases had violated American restrictions but also that the aircraft were now �blockable.� That means they could theoretically be prevented from leaving airports of American allies and other countries that have civil aviation agreements with Iran but that wish to avoid running afoul of the sanctions or antagonizing the United States government.

On Tuesday, the head of Iran�s civil aviation authority said an American effort to have the planes impounded or to thwart Mahan Air�s plans to fly them abroad would not be tolerated.

�America does not have the right to stop our planes on international trips,� the official, Alireza Jahangirian, was quoted as saying by the Iranian Students� News Agency.

According to its website, Mahan Air flies from Tehran to a couple of dozen points in Asia, Europe and the Middle East.

It is unclear how far the dispute will go or whether it will further complicate the work of international negotiators facing a June 30 deadline in the nuclear talks. They are seeking to complete an agreement that would curtail Iran�s nuclear abilities in exchange for an end to the Western and United Nations Security Council sanctions that have hurt the country�s economy for years.

While Airbus is a European company, its planes have many American-made parts that are covered under provisions of United States sanctions that restrict technology exports to Iran.

�You have these big pieces of technology, which the U.S. has some jurisdictional power over,� said Farhad R. Alavi, managing partner of Akrivis Law Group in Washington, which specializes in international sanctions law. By asserting the possibility that the planes could be blocked from flying, Mr. Alavi said, �the U.S. wants to send a signal that Iran is not open for business.�

Still, critics of the Obama administration have said it is so eager to reach a nuclear agreement that it is willing to overlook sanctions infractions and other disputes with Iran in the interest of a successful outcome to negotiations. Administration officials have rejected the criticism.

In a June 1 report made public on Tuesday, the United Nations committee responsible for monitoring the Security Council�s sanctions on Iran suggested that the prospect of a nuclear agreement might be dissuading some countries from complaining about Iranian violations.

The report said a drop in reported violations since a preliminary framework agreement on the nuclear issue was reached with Iran in April might be partly attributable to a decrease in violations by Iran. But the report said it might also reflect �restraint on the part of member states so as not to affect the negotiations process.�

This article was written by Rick Gladstone for The New York Times on June 9, 2015.