The United States Thursday rejected as "baseless" spy charges by Iran against an American-Iranian journalist Roxana Saberi. She has been detained by authorities in that country since January.

The State Department normally declines comment on intelligence matters, but it is flatly dismissing the Iranian spy charges against Roxana Saberi as baseless and again calling for her early release.

The 31-year-old dual American-Iranian citizen, who had been working in Iran for news outlets including National Public Radio and the British Broadcasting Corporation, was arrested in late January - initially accused of operating without press credentials.

Wednesday, Iranian prosecutors announced the espionage case, accusing her of using journalism as a cover for passing information to U.S. intelligence, and saying she had "accepted" the charges against her.

At a news briefing, State Department Acting Spokesman Robert Wood rejected the charges and said he gives "no credence at all" to the notion Saberi had admitted to spying.

"We're deeply concerned about the Iranian government announcement that Roxana Saberi has been charged with espionage," Wood said.  "This charge is baseless. It's without foundation. And what we want to see Iran do is release Roxana Saberi so she can go back to her family."

Secretary of State Hillary Clinton said Wednesday she was deeply concerned about the news of the espionage charge and urged Saberi's immediate release.

Saberi is one of three Americans either detained or believed missing in Iran who were mentioned in a diplomatic note passed to Iranian officials by the Secretary's party at the Hague conference on Afghanistan late last month.

The Obama administration has made several overtures for direct dialogue with Iran in recent weeks and officials here have said the action against Saberi is hardly the response they are looking for.

Wednesday, the State Department said the United States will, from now on, play a direct role in big-power contacts with Iran on its nuclear program.

With a single exception, the Bush administration had deferred to European allies in nuclear talks with Iran, insisting that Iran suspend uranium enrichment as a condition for direct dialogue.

Tehran authorities Thursday said the enrichment program, believed by the United States to be weapons-related, has been expanded further - a development State Department Spokesman Wood said poses a very serious problem.

"Engaging with Iran is something we've said we will now do without preconditions," Wood said.  "But there are certain obligations Iran has. We've said all along Iran is entitled to have a civilian nuclear program - but with that program comes responsibilities. And Iran has not been forthcoming with regard to some of the concerns the international community has about its program."

The United States along with fellow permanent U.N. Security Council member countries and Germany said earlier this week they will invite Iran to a joint meeting try to seek a diplomatic solution to the nuclear issue. Iran, which has denied having a secret nuclear weapons program, says it will review the offer and decide how to respond after examining details of the invitation.