WASHINGTON - The United States on Tuesday denied reports about its request for an exchange of prisoners with Iran in its efforts to secure the release of a former American Marine.

"Those reports are not accurate," State Department spokesman Jeffrey Rathke told reporters at a daily news briefing, adding "The US government has not proposed a prisoner exchange for Mr. Hekmati. It's not true."

Amir Hekmati, an Iranian-American, was arrested in August 2011 on a visit to his family in Iran over the charge of being a Central Intelligence Agency spy.

The former Marine was condemned to death in January 2012 but the sentence was overturned two months later by Iran's Supreme Court after his appeal. The country's Revolutionary Court then charged him with "cooperating with hostile governments" and sentenced him to 10 years in prison.

Tehran is known to be holding two other Americans -- Saeed Abedini, a pastor, and Jason Rezaian, a Washington Post reporter, while Robert Levinson, a retired agent of the Federal Bureau of Investigation, has gone missing in the Islamic republic since 2007.

"We do, however, call on the Iranian government to release Amir Hekmati immediately, as well as detained US citizens Saeed Abedini and Jason Rezaian, and to assist us in locating Robert Levinson," Rathke said.

Hekmati's attorney told Iran's Tasnim news agency on Tuesday that the US has asked Iran to make a swap for his client through its Interest Section in Tehran, Iran's capital.

The Swiss embassy in Tehran represents Washington's interests, as US and Iran have cut off diplomatic ties since 1980.