One of three Americans held for more than a year in Iran suspected of spying has been freed, her lawyer has said.

"I am inside Evin prison, doing her paperwork. She has been released and is heading towards the Swiss Embassy," Sarah Shourd's lawyer, Masoud Shafie, said from the jail where she had been held.

Shourd and two male companions were arrested near Iran's border with Iraq in July 2009. Their families say they were on a mountain hike in northern Iraq at the time of their arrest.

President Barack Obama said he remained hopeful that Tehran would demonstrate "renewed compassion" by freeing two other Americans.