CAIRO, Egypt - An Iranian American academic who works at a Washington-based institute is being held in a notorious prison after being prohibited from leaving Iran for more than four months, the institute and her husband said yesterday.

Haleh Esfandiari, the director of the Middle East program at the Woodrow Wilson Center for Scholars, was sent Tuesday to Evin prison after she arrived at Iran's Intelligence Ministry for questioning, the center said.

Iran has not confirmed that it is detaining Esfandiari, and officials in Tehran could not be reached yesterday.

"This is extremely disturbing news," Esfandiari's husband, Shaul Bakhash, said by phone from their home in Potomac, Md. "I never expected they would jail a 67-year-old woman for no reason whatsoever."

Her arrest comes as Washington and Tehran are locked in a standoff over Iran's nuclear program and involvement in Iraq. Although the two countries ceased formal relations after the 1979 seizure of the U.S. Embassy in Tehran, tensions have risen sharply in the last year.

Other Iranian Americans also have been prohibited from leaving Iran in recent months, including journalist Parnaz Azima, who works for the U.S.-funded Radio Farda. Another American, former FBI agent Robert Levinson, disappeared in March after going to Iran's resort island of Kish, and his whereabouts are unknown. Iran says it is investigating.

State Department spokesman Sean McCormack said that "if the regime is willing to harass these innocent people, it's just an insight into the kind of government we're dealing with."

The Wilson Center said three masked men holding knives had threatened to kill Esfandiari, who was in Tehran visiting her 93-year-old mother, on Dec. 30 as she was going to the airport. They took her baggage, including her U.S. and Iranian passports, the center said.

For several weeks, she was interrogated by authorities for up to eight hours a day, and allowed to go home, the center said. Most questions focused on the Wilson Center's activities.

Former Rep. Lee Hamilton, director of the Wilson Center, wrote to Iranian President Mahmoud Ahmadinejad on Feb. 20 to ask that Esfandiari be allowed to return to the United States. But Hamilton - cochairman of the Iraq Study Group, which recommended that the Bush administration talk to Iran - received no response, the center said.