The US on Friday asked Iran to release three detained American hikers on humanitarian grounds immediately, even as it claimed that the Iranian nuclear scientist came here and left the country on his own will. "He (Shahram Amiri) chose to come here, and we supported him in coming here. He chose to go home, and we freely allowed him to do that. That is what we do in this country. He came here of his own free will, and he has departed and returned to Iran under his own free will," the state department spokesman, Mr P.J. Crowley, told reporters. "It is on that basis that we continue to believe that Iran should release our three hikers. They are exactly as we have described them - three hikers who walked up to an unmarked border. They are in custody. They have not been charged. We believe strongly they should be released on humanitarian grounds," Mr Crowley said. Strongly refuting allegation by Amiri that he was abducted, Crowley said: "I think we have every confidence that he was here by his own decision. He departed under his own decision. I don't know that we can say why he left Iran, why he chose to return. I don't think that there's going to be any particular propaganda value in this." Noting that this point out the dichotomy, he said: "We allow people to come here, go home. We have our own citizens who have traveled to the region and are now in Iranian custody. We are also obviously conscious of the case of Robert Levinson." The US has sought Iranian cooperation to try to determine his whereabouts and welfare, it has received no cooperation from Iran, he said. "So Amiri - his return to Iran, should underscore that we expect the same kind of treatment for our citizens when they travel to Iran," he said. Crowley asserted that three US citizens were not guilty of any crime other than crossing an unmarked border. "They have not been charged. We are coming up on the first anniversary of their incarceration. We want to see them released and returned to the United States," he said. "This is an example where Iran demands respect from the international community. But we have shown with an Iranian citizen who chose to come here and have chosen to go home that he's free to do so. We would expect the same consideration when it comes to our citizens when they travel to the region and up to the border between Iraq and Iran," Crowley said. The mothers of the three hikers were in Iran recently and made a direct appeal to Iranian authorities. "But to the extent that the Iranian people are seeing Amiri return to Iran, we would like to have the same opportunity to welcome home to our country the three hikers and have information, at the same time, on the status of Levinson," Crowley said.