But then Iranian authorities announced that detained American journalist Roxana Saberi had been charged with spying for the U.S. and would be put on trial next week. Washington has appealed for her release since she was detained more than two months ago.
In another example of mixed signals from Tehran, Iran President Mahmoud Ahmadinejad said Thursday his country is open to talks offered by the U.S. and other countries over its nuclear program, if the negotiations are based on "respect" for Iran's rights.
He says "the Iranian nation has always been for talks," but that negotiations have "to be based on justice and respecting rights."
For a generation, the official exchanges between the U.S. and Iran have largely been limited to talks over security in Iraq and Afghanistan. Diplomatic relations had ended in the wake of the 1979 Islamic Revolution and subsequent hostage-taking at the U.S. Embassy in Tehran.
As a presidential candidate, Barack Obama said he was willing to open direct talks with Iran. Last month, he recorded a video addressed to the Iranian people in which he said the U.S. was prepared to end years of strained relations if Tehran toned down its bellicose rhetoric.
The State Department said Wednesday the United States had decided to be present at the table "from now on" when senior diplomats from the five permanent members of the U.N. Security Council and Germany meet with Iranian officials to discuss the nuclear issue.
Secretary of State Hillary Rodham Clinton said the United States would now be a "full participant" rather than an observer in the talks, which include the other four permanent members of the U.N. Security Council - Britain, China, France and Russia - along with Germany.
"We believe that pursuing very careful engagement on a range of issues that affect our interests and the interests of the world with Iran makes sense," Clinton said. "There is nothing more important than trying to convince Iran to cease its efforts to obtain a nuclear weapon."
The six-nation group said in London on Wednesday that it would invite Iran to attend a new round of talks that have been deadlocked over Iran's refusal to stop developing components that can be used to make nuclear weapons. Iran denies charges it is seeking atomic arms and insists its program is designed to produce power.
The group has offered Iran a package of incentives to stop enriching and reprocessing uranium. Tehran has thus far rebuffed the offer despite the fact that its refusal has led to the imposition of three rounds of economic, trade and financial sanctions by the U.N. Security Council.
State Department spokesman Robert Wood said the administration believes a diplomatic resolution to the nuclear issue requires "a willingness to engage directly with each other on the basis of mutual respect and mutual interests."
"We hope that the government of Iran chooses to reciprocate," he added.
Yet, at the same time, an Iranian judge ordered Saberi to go to trial. Saberi, who grew up in Fargo, N.D., and is a dual citizen of the U.S. and Iran, has been living in Iran for six years. She has reported from there for several news organizations, including National Public Radio and the British Broadcasting Corp.
An investigative judge involved in the case told state TV that Saberi was passing classified information to U.S. intelligence services, an accusation that Wood said Thursday was "baseless" and "without foundation."
"What we want to see Iran do is to release Roxana Saberi so that she can go back to her family," he said. "We'd like to see her released as a humanitarian gesture."
Saberi was one of three missing or detained Americans mentioned in a written message passed by U.S. officials directly to Iranian diplomats last month at an international conference on Afghanistan in The Hague, Netherlands, that Clinton attended. Iran has yet to respond to the message, which sought information about the three and was another break with past U.S. policy.
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