U.S. Secretary of State Hillary Rodham Clinton is again calling on Iran to release three Americans as a senior Iranian prosecutor said they have been accused of espionage.

Clinton said Monday the U.S. believes "strongly that there is no evidence to support any charge whatsoever."

The three Americans were arrested July 31 after straying over the Iranian border from northern Iraq. The U.S. government and their families say there were on a hiking vacation and crossed accidentally.

Clinton said the U.S. would continue to make that case through the Swiss channels who represent U.S. interests in Tehran. She spoke at a news conference in Berlin, where she is marking the 20-year anniversary of the fall of the Berlin Wall.