Three Americans who were arrested by Iranian border guards in late July after crossing into Iran from neighboring Iraq have been charged with espionage, a top Iranian prosecutor said Monday. Abbas Jafari Dowlatabadi said that an investigation is continuing and that a 'final decision' about their case would be announced soon, a state-run news agency reported, leaving it unclear whether Iran would go ahead with a formal trial on spying charges, which carry the death penalty. The three -- Shane Bauer, Joshua Fattal and Sarah Shourd -- were hiking in the mountains of Iraq's northern Kurdish region on July 31 when, according to their families, they strayed across the border accidentally. Authorities in Tehran confirmed three days later that the three had been arrested, and an Iranian Arabic-language television network quoted police sources as saying they were 'CIA agents.' In Berlin, where she was attending ceremonies marking the 20th anniversary of the fall of the Berlin Wall, Secretary of State Hillary Rodham Clinton called for the release of the Americans. 'We believe strongly that there is no evidence to support any charge whatsoever,' Clinton said at a news conference. 'And we would renew our request on behalf of these three young people and their families that the Iranian government exercise compassion and release them so they can return home, and we will continue to make that case.' President Mahmoud Ahmadinejad, asked about the case Monday during a visit to Turkey, said he hoped the Americans could persuade Iran's judiciary that they are not guilty of espionage, but he suggested that they deserve at least some punishment for entering the country illegally. 'If drivers in a city pass through a red light and wreck the traffic, can you ask the police in the name of humanity not to punish them?' Ahmadinejad said at a news conference in Istanbul. He added, 'Whether they are spies or not must be determined by the courts.' Bauer, 27, and Shourd, 31, are freelance journalists who were living together in Damascus, Syria, where Shourd also taught English and was studying Arabic, friends and relatives said. Fattal, 27, is a friend of Bauer's who was visiting the Middle East to explore his father's roots in Iraq, friends said. All three graduated from the University of California at Berkeley. Bauer, an Arabic speaker from Minnesota who graduated from Berkeley in 2007 with a degree in Arabic and peace and conflict studies, is a Middle East correspondent for New American Media and has written for publications including the Nation magazine, the San Francisco Chronicle, the Los Angeles Times and Slate.com. Shourd has written for Brave New Traveler, an online travel magazine. She identified herself on the magazine's Web site as a 'teacher-activist-writer from California currently based in the Middle East.' After their arrest, the three were moved to Tehran, where they are being held in the notorious Evin prison. 'The three are charged with espionage,' Jafari Dowlatabadi told the Islamic Republic News Agency on Monday. 'Investigations continue into the three detained Americans in Iran.' According to Iran's English-language Press TV, the prosecutor added that 'the final decision about the detained U.S. citizens would soon be announced.' Late last month, Iranian authorities permitted a Swiss diplomat in Tehran to visit the three for a second time. In the absence of U.S. diplomatic relations with Iran, which were severed following the November 1979 takeover of the U.S. Embassy in Tehran, Switzerland represents U.S. interests in Iran. Over the weekend, the three Americans' families released statements from them at vigils marking their 100th day in captivity. 'I know you are fighting for me, and it makes me proud,' Shourd said, according to her family. 'I am hanging in there with you.' Special correspondent Kay Armin Serjoie in Tehran contributed to this report. 