TEHRAN - An Iranian-American journalist detained in Iran, Roxana Saberi, has been charged with espionage on behalf of the United States and her trial will start next week, Iranian media reported on Wednesday.

In Washington, U.S. Secretary of State Hillary Clinton said she was very concerned by reports of the charges against Saberi and demanded her immediate release.

The new U.S. administration of President Barack Obama is trying to reach out to the Islamic Republic, offering a new beginning of engagement after three decades of mutual mistrust.

Shortly after the news about Saberi, six major powers meeting in London said they would invite Iran for talks to seek a diplomatic solution to the dispute over its nuclear programme and, in a major shift, the United States would take part.

Saberi, 31, who was born in the United States and has reported for the BBC, National Public Radio and other media, was arrested in January for working in Iran after her press credentials had expired.

Iran's deputy prosecutor for security issues, Hassan Haddad, said she had confessed to taking part in espionage activities, Iran's English-language Press TV said.

She has been charged and a branch of the Revolutionary Court is reviewing her case now, ISNA news agency quoted him as saying, referring to a court which handles security issues.

The judge in the case told state television: Journalism for this accused ... was a cover to collect information and intelligence and transfer them to America's intelligence service. The television only gave his last name, Heydarifard.

He said Saberi would go on trial next week.

Her lawyer, Abdolsamad Khorramshahi, told Reuters: As they have announced, they have accused her of espionage. But he said he had not yet received official word about the charges.

Under Iran's penal code, espionage can carry the death penalty. Last November Iran executed an Iranian businessman convicted of spying on the military for Israel.

We are deeply concerned by the news we are hearing... We wish for a speedy release and return to her family, Clinton told reporters in Washington.

BROTHERS JAILED

Washington cut ties with Tehran shortly after the Islamic revolution in 1979, but Obama has offered to extend a hand of peace if Iran unclenches its fist.

Iran says it wants to see real change in Washington's policies, away from those of former President George W. Bush, who led a drive to isolate Tehran because of nuclear work the West suspects has military aims, a charge Iran denies.

Saberi's parents visited her in Tehran's Evin jail on Monday, after arriving from the United States. Evin is a jail where rights groups say political prisoners are usually taken.

Last month, Reza and Kiko Saberi appealed to Supreme Leader Ayatollah Ali Khamenei for their daughter's release, saying she was in a critical mental condition.

She is a citizen of both the United States and Iran. But Tehran does not recognise dual nationality.

This issue has no impact on reviewing her case in Iran's judicial system, Haddad said, adding one person who used to provide Saberi with intelligence had also been arrested.

In another case that has caused concern in the West, state television said a court had upheld the jail sentences on two Iranian brothers accused of involvement in a U.S.-funded plot to overthrow the Islamic system of government.

Arash and Kamiar Alaei, who are both doctors, were arrested in 2008 and later jailed for six and three years respectively.

Iran often accuses the West of seeking to undermine the Islamic state through a soft or velvet revolution with the help of intellectuals and others inside the country.

Diplomats and human rights groups say Iran has cracked down on dissenting voices since President Mahmoud Ahmadinejad came to power in 2005, possibly in response to Western pressure on Tehran to halt its disputed nuclear work.