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Iran also has started producing uranium at a higher level than its main stockpile — a move that would jump-start the creation of highly enriched, weapons-grade uranium, should it chose to go that route. And it is moving its higher-enriched operation into an underground bunker that it says is safe from attack.

Tehran is under four sets of U.N. Security Council sanctions because of its refusal to heed international concerns about its nuclear programs, as well as penalties imposed by the United States and Western nations meant to force it into dialogue.

The European Union last week imposed an oil embargo on Iran and froze the assets of its central bank. In December, the United States said it would bar financial institutions from the U.S. market if they do business with Iran’s central bank.

AP video reporter Philipp Jenne contributed to this article.