This story has been updated.
Shahram Amiri, the Iranian nuclear scientist in the middle of a high-stakes battle between Washington and Tehran, has taken refuge in a Pakistani embassy building in Washington, D.C. and will leave for Iran within the next 48 hours.
Iranian official Ali Shirazi confirmed to ABC News that Amiri is now in the Iranian interests section building, which is under the auspices of the Pakistani diplomatic mission to the U.S. A senior Pakistani official told ABC News that Amiri arrived at the Iranian building at 6:30 p.m. Monday and asked to go home. Both Iranian and Pakistani officials told ABC News that Amiri will leave the U.S. within the next 24 to 48 hours.
Secretary of State Hillary Clinton said Amiri has been in the United States "of his own free will."
"His is free to go," said Clinton. "He was free to come. These decisions are his alone to make."
Clinton said that Amiri was actually scheduled to travel to Iran on Monday "but was unable to make all the of the necessary arrangements to reach Iran through transit countries."
Another U.S. official said Amiri's decision to return home "gives the lie to the idea he was tortured or imprisoned. He can tell any story he wants -- but that won't make it true." The official said Amiri "came to this country freely, he live there freely, and he has chosen freely to return to Iran."
While Iranian authorities claim Amiri was abducted in Saudi Arabia in 2009 and brought to the U.S. against his will, U.S. intelligence officials say Amiri defected to the U.S. voluntarily after working for several years as a CIA spy and providing crucial details about Iran's burgeoning nuclear weapons program.
According to people in the U.S. intelligence community briefed by the CIA, the Iranian government threatened to harm Amiri's family unless he returned home. He left a wife and son behind.
In two videos released at the end of June, Amiri claimed to have "escaped" U.S. intelligence and said he was on his way back to Iran.
On the videos, Amiri claimed that he escaped "U.S. intelligence officers in Virginia." He said he was now in a "safe place" but that he was in "danger and could possibly be arrested again by U.S. intelligence officers at any moment." He has also claimed that he was tortured by U.S. officials.
"In case anything happens to me or if I do not make it back home safely, the responsibility will solely rest on the officials of the United States," Amiri said in a video posted to YouTube, which was apparently recorded June 14.
After the release of the videos, a U.S. official disputed Amiri's claims.
"The guy's ability to make and release messages is clear proof that he hasn't been held in the United States against his will," said the official. "That's not the way it works -- we don't have to compel people to defect. Maybe he's just trying to build a story for the folks back home. The fact that he can say what he wants doesn't make his statements true. He's shown to the world that he has the power to make choices -- even bad ones."
The second of the two videos aired on Iranian state television, continuing the effort of Tehran to show Amiri was kidnapped and brought to the U.S. against his will.
In fact, U.S. officials say, Amiri was a key spy inside the Iranian nuclear program for several years before his defection.