Iran says it will continue to negotiate over its nuclear program, despite a U.S. decision to expand its blacklist to include more than a dozen firms doing business with Iran's national tanker company.

Iran, if you remember, struck a temporary six-month deal with world powers that paused some aspects of its nuclear program in exchange for some sanctions relief. Iran had said that any new sanctions would kill the prospects for a long-term deal.

On Thursday, the AP reported, the United States said it was freezing the assets of "firms in Panama, Singapore, Ukraine and elsewhere for maintaining covert business with Iran's national tanker company." As the BBC reports, Iranian negotiators walked out of talks, saying the move "went against the spirit of an agreement brokered in Geneva."

The AP reports that on Sunday, Foreign Minister Mohammad Javad Zarif called the move "improper" but said his country would continue to talk.

"We will continue Geneva talks. We will show proper, calculated, purposeful and smart reaction toward any improper and unconstructive action," Zarif wrote on Facebook "Over the past days, improper actions were carried out by Americans that we responded in a proper way."

He added: "Talks and reaching a conclusion is a difficult job and it will definitely have ups and downs. ... We had predicted this from the first day."

The Obama administration, meanwhile, has asked Congress to delay passing any new laws that impose new sanctions on Iran. The expansion of the black list was done under existing law.

Update at 10:54 a.m. ET. Process Has Derailed, 'Not Died':

In an interview with CBS' Elizabeth Palmer, which aired on Face the Nation, Zarif said the Iranians first learned of the expanded sanctions minutes before it was announced publicly.

Palmer asked Zarif if that made him angry.

"Angry is not a part of diplomacy," Zarif said. "Angry is human and I get angry, I get distressed, I get saddened to see people not understanding... I am saddened by that, but we took a decision to give a pause to the discussions - technical discussions - to have a reassessment, to seek clarification what is the intention because the statement coming from the Treasury during the past few days were not helpful."

Zarif said the process had been derailed by the U.S. action, but "the process has not died."

"We are trying to put it back and to correct the path, and continue the negotiations because I believe there is a lot at stake for everybody," he said.

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