It marked the latest effort by President Barack Obama's administration to try to patch up with Iran, which has been an arch US foe since its 1979 Islamic Revolution.

The so-called "P5 plus-one" -- UN Security Council permanent members Britain, China, France, Russia and the United States along with Germany -- said in a joint statement in London they would ask Iran for direct talks.

Secretary of State Hillary Clinton said that William Burns, the undersecretary for political affairs, would now take part in the dialogue "as a full participant, not just as an observer."

"Obviously, we believe that pursuing very careful engagement on a range of issues that affect our interests -- and the interests of the world -- with Iran make sense," Clinton told reporters.

"There's nothing more important than trying to convince Iran to cease its effort to obtain nuclear weapons," she said after meeting with her Panamanian counterpart, Samuel Lewis Navarro.

Clinton's predecessor, Condoleezza Rice, had set preconditions to any P5 plus-one meetings involving Iran. Burns held only one such meeting in the presence of the Iranian negotiator, in July last year.

The new US engagement with Iran comes despite concerns after Tehran charged a US-Iranian journalist with espionage on Wednesday.

Prosecutors accused 31-year-old Roxana Saberi -- who worked for US National Public Radio, the BBC and Fox News -- of spying "under the guise of being a reporter." She has dual nationality, which Iran does not recognize.

Clinton voiced hope for her "speedy release and return to her family."

"We are deeply concerned by the news that we are hearing," Clinton said.

State Department spokesman Robert Wood rejected criticism that the United States was moving too quickly with Iran, which has not responded to an earlier message on ways to improve relations.

Wood said the United States was "living up to our commitments to reach out to Iran" and hoped that Tehran would respond in turn.

"A diplomatic solution necessitates a willingness to engage directly with each other on the basis of mutual respect and mutual interests, and we hope that the government of Iran chooses to reciprocate," Wood told reporters.

"If Iran accepts, we hope this will be the occasion to seriously engage Iran on how to break the logjam of recent years and work in a cooperative manner to resolve the outstanding international concerns about its nuclear program."

Obama, voicing hope to turn a new page, sent an unprecedented video message last month for the Persian New Year -- a sharp break from predecessor George W. Bush who branded Tehran as part of an "axis of evil."

Iran has repeatedly denied that it intends to build a nuclear bomb. But six years of probes by the International Atomic Energy Agency -- the UN nuclear watchdog -- have been unable to confirm whether the program is peaceful.

Following Obama's inauguration in January, the six powers said they were ready to engage in direct dialogue with Iran but had not talked of a formal invitation.

The P5 plus-one said it had tasked EU foreign policy chief Javier Solana to extend the invitation to Iran.

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