Gregory Korte

USA TODAY

WASHINGTON — The United States imposed a new round of sanctions on companies doing business with Iran on Friday, alleging that they're helping Iran build its nuclear program, support terrorism and evade sanctions.

The new sanctions come even as Western diplomats say they have made progress on nuclear talks and have even relaxed some broader economic sanctions against Iran.

"Our actions today and since the start of the talks are consistent with our commitments under the Joint Plan of Action, which provided limited relief of certain sanctions in exchange for Iranian steps that halted its nuclear program and rolled it back in key respects," said National Security Council spokeswoman Caitlin Hayden in a statement.

As negotiators failed to meet a July 20 deadline for a deal, Secretary of State John Kerry said the United States would extend negotiations with Iran for four more months. Iran committed to stopping its work on a nuclear program, and in exchange, the United States agreed to release $2.8 billion in oil money frozen in Western bank accounts.

But at the same time, U.S. officials say, Iranian entities continued to evade the previous sanctions put in place as early as 2007. David Cohen, a Treasury undersecretary for counterterrorism, said the latest move was more about enforcing existing sanctions than escalating economic pressure.

The update to the sanctions list "reflects our continuing determination to take action against anyone, anywhere, who violates our sanctions," Cohen said in a statement. "As we fulfill our commitment to provide targeted sanctions relief, we remain committed to enforcing existing sanctions against Iran."

For example, Treasury officials say companies based in Turkey, Thailand and the United Arab Emirates have served as front companies to help Iranian Mahan Air to purchase airplane engines, tires and other parts. Mahan Air was placed on a terrorism-related sanctions list in 2011 for its support of Iran's Islamic Revolutionary Guard Corps.

Two other Iranian airlines, Majan Air and Caspian Air, are accused of ferrying Iranian arms to Syria and were added to the list Friday.

Added to the sanctions list Friday: eight individuals, six ships, five banks and 15 other entities. The sanctions were announced by the State and Treasury departments.

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