VIENNA — Iran and six world powers on Thursday announced that they have agreed on a plan meant to produce a comprehensive deal that reduces concerns about Tehran's nuclear ambitions. Officials of both sides describing their plans as "very productive."

In a joint statement, they said the next round of negotiations would begin in Vienna on March. 17.

"We've identified the issues we need to address for a comprehensive and final agreement," said Catherine Ashton, the EU's top diplomat who convened the talks between Iran and the six powers — the United States, Russia, China, Britain, France and Germany .

"It won't be easy, but we've gotten off to a good start," she said in a statement later read in Farsi by Iranian Foreign Minister Mohammad Javad Zarif.

Expectations of major progress from the three days of talks in Vienna were modest because the two sides have widely differing demands.

The six want Tehran to agree to significant cuts in its nuclear program to reduce concerns it could be turned quickly to weapons use.

Iran is opposed, saying it has no interest in such weapons, but the six powers say that Iran must come to an agreement if it wants a full end to sanctions crippling its economy.

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AP reporter Margaret Childs in Vienna contributed to this report.