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An Iranian airline, backed by the country's notorious Revolutionary Guard and used to ferry weapons and fighters to support Syria's government, has acquired rights to fly commercial routes in more than a dozen European and Asian countries in spite of U.S. terror-related sanctions.

The agreement Iran and six other world powers signed last year ended some of the sanctions that had punished and isolated Iran for its nuclear program. But sanctions for ballistic missile research, terrorism, human rights violations and money laundering remain in place.

Mahan Air, the country's second-largest carrier, is under terror-related sanctions. The U.S. has accused the company of providing "transportation, funds transfers and personnel travel services" to the Revolutionary Guard's elite Quds Forces, flying them and weapons to Syria to train Hezbollah militants, Syrian army troops and others.

Many countries honored the U.S. terror sanctions and blocked Mahan Air. But weeks before the nuclear deal was signed in July 2015, the airline announced it was launching a route to Munich — its second German destination. A wave of new routes to 15 countries followed, including France, Russia, China and Italy. France and Denmark were added in June 2016, and talks continue to add more routes in Europe.

A U.S. Treasury official told The Associated Press that the U.S. has been trying to get those countries to cooperate with U.S. efforts to block the airline's financial network, but has met with stiff resistance.

Washington doesn't want to restrict travel to and from Iran, the official said, noting that the country's main carrier, Iran Air, can fly around the world since the nuclear deal was implemented in January. The official was not authorized to discuss the issue publicly and spoke on condition of anonymity.

"By letting Mahan in, the Europeans are forgoing a critical pressure tool they have in their arsenal of nonmilitary coercive measures to pressure Iran and (Syrian President Bashar) Assad," said Emanuele Ottolenghi, an Iran expert at the Center on Sanctions and Illicit Finance at the bipartisan Foundation for Defense of Democracies.

But the U.S. has no leverage to change EU laws allowing Mahan in. All it can do is ask the countries to ban Mahan and go after companies providing services to the airline, including banks, baggage handlers and cargo and freight companies.

A spokeswoman for the European Union said Mahan Air is not under EU sanction and the U.S. has no jurisdiction. In 2014, the European Commission allowed those deemed safe commercial air transport operators — including Mahan Air — to fly to, from or within the EU.

The EU has also ignored U.S. terror sanctions and last week lifted its own on Bank Saderat, which Washington accuses of transferring money to groups it considers terror organizations, such as Hezbollah's militant wing and Hamas.

"How many dead Syrians does it take for the Europeans to think there is a threat?" said Rep. Brad Sherman, D-Calif., who wants the EU to designate Mahan as a terrorist entity.

In May, Sherman and two dozen other members of Congress wrote David O'Sullivan, the EU ambassador to the U.S. urging the EU to "promptly end Mahan Air's operations in Europe," saying that doing so would "signal to European businesses that the EU will remain vigilant in acting against Iranian companies supporting terrorism and Assad's regime."

Mahan Air officials in Tehran declined to speak to The Associated Press.

The sanctions against Mahan say the airline provided financial, material and technological support to the Quds Force, the Revolutionary Guard Corps' special forces responsible for operations outside of Iran, including in Iraq and Syria. This year, sanctions were extended to a number of entities providing services to the airline — mainly in Dubai, Ukraine and the United Kingdom.

Mahan has denied the charges. Its website notes it is private and "it does not belong to any governmental or military bodies or to any political party or individuals."

Sanctions against five commercial and cargo carriers, including Iran Air, the country's largest commercial airline, were lifted in January following implementation of the country's nuclear agreement.

Iran's Revolutionary Guard Corps, or IRGC, is a vast, powerful military conglomerate, with naval, air and ground components organized in parallel to the conventional Iranian military. It is the country's biggest economic player, with a hand in virtually every sector, from oil and gas to auto-making, telecommunications, construction, farming and beyond.

The airline's current chairman and chief executive, Hamid Arabnejad, is a close affiliate of the IRGC and is believed to still have a close relationship with the division that spawned the Quds Force. The U.S. sanctioned Arabnejad in 2013 for having "been instrumental in facilitating the shipment of illicit cargo to Syria on Mahan Air aircraft."

Sanctioned foreign governments, companies or individuals are generally barred from doing business with U.S. citizens and businesses, or with foreign entities operating in the American financial system. The restrictions are usually accompanied by asset and property freezes as well as visa bans.

Mahan Air flies to Dubai International Airport twice daily from Tehran. The airport, the world's busiest for international travel, declined to discuss Mahan Air, referring questions to federal authorities, who also declined comment.

The Treasury Department said plane spotters have seen Mahan Air flights land in Syria almost daily.

"We're not saying Mahan Air assists the IRGC; we'd say Mahan Air is the IRGC — and we have to give notice to our friends in Europe," Sherman said. "This idea that we can allow Mahan Air to do whatever it wants just because there are temporary restrictions on the nuclear deal — that wasn't the deal."

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Associated Press writer Jon Gambrell in Dubai contributed to this report.