Apple Daily newspaper of Hong Kong quoted the director as saying that the sex scenes in were emotionally intense. "Filming the sex scenes left me on the verge of nearly breaking down," Lee was quoted saying, adding that he was moved to tears when revisiting the set after filming.
"We had just filmed sex scenes in that place. When I saw the empty house in the camera monitor, I couldn't stand it. It's the first time I reacted that way on a movie set," the director said.
The Taiwanese director, who won an Oscar for best director for "Brokeback Mountain" in 2006, was speaking from Venice, where "Lust, Caution" is competing for the top Golden Lion prize at the Venice Film Festival. The movie was screened in Venice last Thursday but has not been released in theaters.
The film received the strictest rating in the U.S., which bans viewers younger than 17.
"Lust, Caution," based on a short story by famed Chinese writer Eileen Chang, is about a group of patriotic students who plot to assassinate the intelligence chief in the Japanese-backed Chinese government during the World War II era.
Hong Kong actor Tony Leung Chiu-wai plays the intelligence official Mr. Yi, while newcomer Tang Wei plays the Chinese student Wang Jiazhi, who seduces Yi to pave way for the assassination. The movie also features Joan Chen from "The Last Emperor" and Chinese-American pop star Leehom Wang.
In a separate interview with Chinese news Web site Sina.com, Lee said he cleared the set to all but four crew members, including himself, while filming the sex scenes involving Leung and Tang.
"The scenes were completely in a very private space," he said.
Lee told Apple Daily that he spent tremendous effort training actress Tang - more so than for Chinese actress Zhang Ziyi when she was a budding star shooting Lee's kung fu hit "Crouching Tiger, Hidden Dragon."
"She (Tang) was picked from 10,000 people. There was three months' training and five months' shooting. I spent a full eight months on her. I've never spent so much effort on one person," Lee was quoted as saying.