Sprawling over 10 hectares in the bustling heart of Tehran, the defunct US embassy to Iran came back under spotlight after "Argo," a movie about how six US diplomats fled Iran at the heat of the Iran hostage crisis in 1979, won the Oscar for best movie recently.

The place, not open to visitors, remains mysterious. Upset by the "exaggerated and unbalanced account of facts" in the movie which failed to show America's wrongdoing, as described by the spokesman for the complex Alireza Rahmenzadeh, Iranian officials lately decided to allow Xinhua reporters inside to prove that the movie was "biased."

The complex, dubbed by Iranians as the "US espionage den," is now controlled and guarded by Basij militia. Passers-by hurry themselves as if they would be suspected of espionage if they linger. Tourists are led to believe that they would be questioned by secret police for taking photos there.

Shabby and full of anti-US graffiti, the walls of the former embassy still can block the din and thick smog in downtown Tehran.

Entering from the east gate, the first building is the former ambassador's residence. The three-storey white building is now the complex's administrative office. Down on the first floor, the hall where the American ambassador used to meet with dignitaries is now turned into a conference room with photos of Iran's late supreme leader Ruhollah Khomeini and current supreme leader Ali Khamenei high on the wall.

The main building, a two-storey red brick structure, looks so much like an old American high school that US diplomats used to nickname it Henderson High, after the first Ambassador who worked in it.

Now the building is called Vezvaee Building after an Iranian martyr. With a statue of liberty standing at the gateway, the staircase to the second floor is covered by colorful mural of Persian heroes fighting US tanks and bombers.

Alireza, the spokesman, said the second floor was a restricted area where American espionage took place. It took him minutes rotating the combination lock to open the heavy metal door, on which hung a large poster featuring a surrendering American soldier.

Behind the door is a corridor that leads to the "glassy room," transparent and walled by two layers of special plastic materials. Huge pipelines vacuum the space between the layers so it's impossible to eavesdrop from outside, while transparency makes it difficult to hide any device inside. "This is where the Ambassador held his secret meetings," Alireza said.

Yet the "glassy room" is not the most secretive facility here. Deep inside the floor, there's a room protected by a bulky high- tech metal door that can only be opened with simultaneous matches of code, iris and body weight.

"Even the student protesters could not enter. So they made a fire and smoked people out from inside," Alireza said. Inside the room are large machines for tapping telephone conversations.

Almost every line of any people of note was tapped, including the Shah's mother, said the spokesman. The Pahlavi royal family had to protest and demand for an untapped line, he said.

Nearby is a smaller room with painting tools and many photos. Alireza said American agents used to forge passports, visas and other fake documents there.

Outside the "forgery room" sits a large bucket full of dust. Alireza grasped a handful of the dust and called it remains of the most important documents of the US embassy.

When protesters breached the premise, embassy staff started to destroy top secrets with paper powdering machines. They were in such a hurry that the machines overworked and broke down. Then they had to switch to shredders, Alireza said.

Later, Iranians recovered the shredded paper and stuck them back piece by piece to form 80 books of American secrets in Iran.

Then Alireza led us to a small steel staircase hidden in a room full of large computers. "Spies traveled between sensitive spots in the embassy trough the secret paths to avoid being noticed by other staff. This is one of them," he said.

He also took us up to an alleged "detention room" on the rooftop, stressing it was the first time that this room was revealed to media. In the room hung some ropes, but it was too dark to see if there were any signs of torture.

Outside the main building, there were facilities like sports center, mosque and education building. Alireza said the complex sometimes hold activities for Basij's student members.

"All the buildings are as they were. We never built anything new because we plan to return this embassy on the day when Iran and America resumes diplomatic relations," he added.