U.S. Secretary of State Hillary Clinton called the reply letter sent by Iran to EU foreign policy chief Catherine Ashton "an important step".

　　"As outlined in Cathy's October letter to Iran, any conversation with Iran has to begin with a discussion of its nuclear program and Iran's response to Cathy's letter does appear to acknowledge and accept that," the top U.S. envoy told reporters after meeting Ashton at the State Department.

　　Iran's letter, sent by its chief nuclear negotiator Saeed Jalili on Tuesday in response to Ashton's October letter offering to resume talks on condition that the Islamic republic sets no preconditions, said it is ready for renewed negotiations with the six powers -- Britain, China, France, Russia, the U.S. and Germany.

　　Clinton demanded Iran's assurances for a "sustained effort" in reaching an outcome once the six powers go ahead with the talks.

　　However, she added that "I think it's fair to say -- of course I'll let Cathy speak for herself -- that we think that this is an important step and we welcome the letter."

　　For her part, Ashton said she was "cautious and optimistic" about the prospect of resumed talks with Iran. She sent her letter to Iran on behalf of the six powers, whose last talks with the country broke down in Istanbul, Turkey in January 2011.

　　"There is a potential possibility that Iran may be ready to start talks. We'll continue to discuss and make sure that what we' re looking at is substantive," she said, adding "But I'm cautious and optimistic at the same time for this."

　　Iran is suspected of seeking nuclear bombs under its nuclear program, but the country counters that its nuclear program is only for peaceful purpose.

　　Washington and the EU have targeted Iran's central bank and oil exports for sanctions in their continuous efforts to press the country to stop its uranium enrichment activities.