Secretary of State Hillary Clinton on Monday implored Iran to release three U.S. hikers it captured and detained at the end of July.

Her renewed, impassioned defense of the hikers -- who Iranian authorities picked up on charges of illegally crossing the border from Iraq's Kurdistan region into Iran -- arrives after Tehran announced this morning it would charge them with espionage. The three U.S. citizens, however, have maintained that the crossing was an innocent mistake.

"We believe strongly that there is no evidence to support any charge [of espionage] whatsoever," Clinton said while in Berlin to celebrate the toppling of the wall that once stood there.

"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," the secretary added.

Diplomatic relations between the United States and Iran have been especially tenuous since U.S. officials discovered Tehran was operating a secret uranium refinement facility in the city of Qom.

International inspectors have since declared that site benign, and world leaders have made progress convincing Iran to suspend its clandestine nuclear program, but Monday's episode portends only more political bickering between U.S. officials and their Iranian counterparts.