TEHRAN, Iran – A detained Iranian-American academic was suddenly released from a notorious Tehran prison Tuesday after spending months behind bars on charges of endangering Iranian national security – allegations her family vehemently denies.

Haleh Esfandiari, director of the Middle East program at the Woodrow Wilson International Center for Scholars, had been jailed in Evin prison since early May after months of interrogation. Her 93-year-old mother used the deed to her Tehran apartment to post bail, relatives said.

“I’m very happy. It was unexpected. I thank all those who made efforts to make it possible for me to go home,” Esfandiari told Iranian television.

Mohammad Shadabi, an official at the Tehran prosecutor’s office, said Esfandiari had been released on $333,000 bail, but he could not say whether she would be allowed to leave Iran.

Esfandiari, 67, was detained Dec. 30 after three masked men holding knives threatened to kill her on her way to Tehran’s airport to fly back to the United States, the Wilson Center has said. The men took her U.S. and Iranian passports, making her unable to leave the country, the center said.

For several weeks, she was interrogated by authorities for up to eight hours a day about the activities of the Middle East Program at the center, the Washington-based foundation said.

Iran charged Esfandiari in May. Since then, her only contact with her family had been brief telephone calls to her mother in which she said she was under stress and having trouble receiving medication for her health conditions, said former Rep. Lee Hamilton, head of the Wilson Center.

The Iranian Intelligence Ministry had accused Esfandiari and her organization of trying to set up networks of Iranians with the ultimate goal of creating a “soft revolution” in Iran. Her husband, Shaul Bakhash, and the Wilson Center denied the allegations.