The mother of Sarah Shourd, one of the three US hikers arrested after apparently straying into Iran four months ago, launched a video campaign yesterday urging clemency for the group.

"This is a time of the year when families come together. This time unites us as children of God," Norah Shourd said in the video directed at Iranian supreme leader Ayatollah Ali Khamenei, and posted on the website www.freethehikers.org.

"They are good people, they did not mean to enter Iran and have deep respect for your ancient and noble civilization... If they entered Iran it was an innocent mistake," she said.

Ms Shourd, 31, Shane Bauer, 27, and Josh Fattal, 27, were arrested on July 31 after allegedly straying into Iranian territory during a hiking trip in Iraq's Kurdistan region.Iran's public prosecutor said in November that the trio faced espionage charges.

On Monday, Foreign Minister Manouchehr Mottaki said the trio, who are held at Tehran's Evin prison in separate cells, will face trial, saying that "interrogation of the three Americans who have illegally entered Iran with suspicious aims is ongoing."

Their friends and relatives deny that they are spies and the United States insists they be released.

"On behalf of the mothers of Shane and Josh, I respectfully apologize and request for your benevolence for this time of the year. Please release our children and return them home to us," said Ms Shourd, her head covered by a shawl in the video.

"The holidays are a time for families to be together. This is not an American value or an Iranian value, it is a human value."