ISTANBUL, Turkey — Iran released an American hiker Tuesday after more than a year in custody but continued to hold two fellow countrymen who are expected to face trial.

Sarah Shourd was freed from Tehran’s Evin Prison on $500,000 bail, according to the office of Tehran prosecutor Abbas Jafari-Dolatabadi. She flew to the Persian Gulf kingdom of Oman and was met there by her mother and uncle, a witness told Reuters news service.

Iranian state television broadcast a brief interview with Shourd, wearing a maroon headscarf and white overcoat, as she boarded what appeared to be a private jet in Tehran.

“”I want to really offer my thanks to everyone in the world, all of the governments and all of the people that have been involved,”” she said, appearing healthy despite reports of medical problems in prison. “”And I especially, particularly want to address President Ahmadinejad and all of the Iranian officials, the religious leaders and thank them for this humanitarian gesture. I’m grateful and I’m very humbled by this moment.””

Shourd, 32, along with friends Shane Bauer and Joshua Fattal, were arrested by Iranian authorities more than 13 months ago during what their relatives say was an ill-fated hiking trip in northern Iraq along the border with Iran.

They were formally charged this week with espionage and illegally entering Iran. The prosecutor said Fattal and Bauer would be held in jail for at least another two months.

“”The case of the remaining two Americans, whose bill of indictment has been drawn up, is referred to court for further investigation,”” the statement said.

The prosecutor’s statement cited Shourd’s medical problems in explaining her release from prison.

“”Based on the reports by her lawyer, our investigators and evidence provided by the government … we decided to take the detainee’s health situation into consideration and grant her bail,”” Jafari-Dolatabadi told Press TV.

Jafari-Dolatabadi said in the statement that Shourd’s backers had put up “”a certified banking receipt”” for the equivalent of $500,000. U.S. government officials have been quoted as saying that no American money would be used for the bail.

In Washington, the White House released a statement by President Barack Obama pleading for the release of Shourd’s companions, noting: “”Shane Bauer and Josh Fattal remain prisoners in Iran who have committed no crime.””

The three Americans’ case has further strained ties between Tehran and Washington, which accuses Iran of pursuing nuclear weapons capabilities and undermining peace in the Middle East. But it has also highlighted factional battles within Iran’s political establishment.

Officials under the authority of President Mahmoud Ahmadinejad originally announced Shourd’s release late last week to much fanfare, inviting journalists to attend a Saturday morning ceremony at a presidential palace. But Jafari-Dolatabadi, who answers to a judiciary controlled by one of Ahmadinejad’s conservative rivals, abruptly canceled the planned release, declaring that she would have to put up bail.

Ahmadinejad is scheduled to arrive in New York later this month for an annual gathering of world leaders at the United Nations.