Iran is to put on trial three US hikers arrested after they "illegally" entered the country four months ago, Foreign Minister Manouchehr Mottaki said on Monday.

"Interrogation of the three Americans who have illegally entered Iran with suspicious aims is ongoing. They will be put on trial by the judiciary and rulings will be made," Mottaki told a news conference carried live on state television.

Shane Bauer, 27, Sarah Shourd, 31, and Josh Fattal, 27, were arrested on July 31 after straying into Iranian territory during a hiking trip in Iraq's Kurdistan region.

In Washington on Monday, US Secretary of State Hillary Clinton urged Iran to free them.

"We appeal to the Iranian leadership to release these three young people and free them as soon as possible," she told reporters.

Iran's public prosecutor said on November 9 the trio faced espionage charges, but Mottaki said a day later that they were charged with illegal entry.

The trio are held at Tehran's Evin prison in separate cells and with few visits allowed. Their friends and relatives denied that they were spies and the United States insisted that they be released.

Clinton has already said the US administration was "exploring every angle" to help them.

Earlier this month scores of prominent international figures also called on Iranian President Mahmoud Ahmadinejad to release the three.

Strained ties

The case has further strained ties between Tehran and Washington which have had no diplomatic relations for nearly three decades.

Washington is also spearheading international efforts to curb Iran's atomic drive as Western powers fear Iran is seeking to acquire nuclear weapons under the guise of a civilian programme -- a charge Tehran vehemently denies.

In response to calls to release the three, Iran has brought up the case of its own nationals detained in the United States and other countries.

Tehran has accused Washington of abducting Shahram Amiri, an Iranian nuclear scientist who went missing in Saudi Arabia during a minor Muslim pilgrimage.

The US State Department declined to comment on the Iranian claims.

On Thursday Iranian media published a list of 11 Iranians they said were being held by the United States or other countries.

Mehr news agency said the foreign ministry is "vigorously" using diplomatic means to obtain the release of the Iranians, three of whom have allegedly been detained in countries outside the United States at Washington's request.

In recent years Iran has detained several US-Iranians on suspicion of harming national security.

One of them, academic Kian Tajbakhsh, was rearrested in the aftermath of the disputed June 12 presidential election and sentenced to 15 years in jail.

Mystery also surrounds the fate former FBI agent Robert Levinson, who went missing on the Iranian island of Kish in March 2007. Iranian officials say they have no information about him.

-AFP