The White House is calling for the release of three Americans being held in Iran on accusations of espionage.

White House press secretary Robert Gibbs said Monday that the three were hiking near the border with Iraq and are innocent. He called on the Iranian government to release them quickly.

A senior Iranian prosecutor accused the three of espionage earlier Monday, the first signal that Tehran intends to put them on trial. The announcement came as Washington and Tehran were maneuvering over a deadlock in negotiations over Iran's nuclear program.