Shourd, left, has been held by Iran for more than a year; her mother says she is suffering from poor health [EPA]

Iran has postponed the planned release of Sarah Shourd, a detained US woman, because it says the legal procedure needed to secure her freedom has not been completed.

"Because the legal procedure on her case is not finished, her release is cancelled," the ILNA news agency quoted Abbas Jafari Dolatabadi, a Tehran prosecutor, as saying on Friday.

"The judiciary does not validate the published news and naturally any decision about the defendants will depend on carrying out the judicial process," Dolatabadi said.

Shourd, along with Shane Bauer and Josh Fattal, were arrested in July 2009 after straying into Iranian territory from Iraq.

The three said that they became lost on a hike in Iraqi Kurdistan but Iran has accused them of being spies.

US authorities insist that they are innocent and say they should be released immediately.

An Iranian government official had said on Thursday that Shourd would be released on Saturday as an act of clemency to mark the end of the Muslim holy month of Ramadan.

Medical problems

Shourd, 31, has told her mother that she is suffering from serious medical problems, including a breast lump and precancerous cervical cells.

Prior to Friday's cancellation, the US state department said it was aware of reports that one of the prisoners would be released, but could not confirm them. 

America has no official presence in Iran, and the official said that the US government had heard nothing from the Swiss embassy in Tehran, which represents US interests in the country.

The detention of the three Americans has added further strain to the already fractious relationship between Tehran and Washington, with Iranian leaders repeatedly attempting to link their fate to that of several Iranians being held by US authorities.

Barack Obama, the US president, and Hillary Clinton, the US secretary of state, have both called for the release of their citizens over the past year. 

Obama said the three were "simply open-minded and adventurous young people who represent the best of America, and of the human spirit".

"I call on the Iranian government to immediately release Sarah, Shane and Josh," he said, adding that their "unjust detention has nothing to do with the issues that continue to divide the United States and the international community from the Iranian government".

Source: Al Jazeera and agencies