When director Kim Jee-woon first started filming his newest historical thriller “The Age of Shadows,” he had set his mind on making a “cold” noir flick featuring a ruthless world of spies.

But the film turned out to be much more “heated” than originally intended, he told reporters after a press screening of the film in Seoul on Tuesday.

Director Kim Jee-woon speaks to reporters at a press conference for film “The Age of Shadows” in Seoul on Thursday. (Yonhap)

His original references had been classics like the 1949 black-and-white thriller “The Third Man” and the 1965 Western espionage flick “The Spy Who Came In from the Cold” -? both set in the Cold War era.

In the course of filming, however, Kim discovered that the period of the Japanese occupation of Korea, in which the film is set, had a completely different atmosphere.

“The occupation era was a time when patriots sacrificed their lives without regret to recover a country that had been lost,” said Kim. “With that story in the center, the film couldn’t help but get heated toward the end.”

Though the film ultimately diverged from what he had originally intended, Kim said he chose to “not force a certain filmic self-consciousness or style” and instead “follow the direction of the story and its characters.”

“The Age of Shadows” is the most recent in a string of historical flicks to hit Korean theaters this year -? including “The Last Princess” and “Operation Chromite.”

Actors Song Kang-ho, Gong Yoo and Han Ji-min speak at a press conference for film “The Age of Shadows” in Seoul on Thursday. (Yonhap)

Set in the 1920s, it chronicles the story of independence fighter Kim Woo-jin, played by actor Gong Yoo, and his group of comrades who hatch a plan to smuggle bombs from Shanghai into the Korean capital in order to overthrow the Japanese government.

Actor Song Kang-ho plays Lee Jeong-chool, a Korean national who has sided with the Japanese. A high-ranking officer in the Japanese police, Lee is responsible for spying on and ultimately capturing the independence fighters.

The film aims to explore the “complexity” of the era, according to director Kim, in which coexisted those who spied for the opposition and those that risked their lives to recover their lost country.

“It tries to show a period in which people had no choice but to become spies,” he said.

It’s not a film that chases who the spy is or isn’t, but shows that anybody can be a spy,” said actor Song.

Actress Han Ji-min stars as independence fighter Yeon Gye-soon. Actor Lee Byung-hun makes a cameo appearance as Jeong Chae-san, leader of the independence fighters.

“The Age of Shadows” has been invited to screen at the 41st annual Toronto International Film Festival, to take place on Sept. 8-18, and the 73rd Venice International Film Festival, set for Aug. 31-Sept. 10.

The cast of film “The Age of Shadows” and director Kim Jee-woon (far right) pose for a photo at a press conference in Seoul on Thursday. (Yonhap)

With a budget of $8.62 billion, it is the first ever Korean-language film to be produced by Warner Bros., which will also helm local distribution. Korean sales company Finecut picked up the film’s international rights in April.

Kim previously directed “I Saw the Devil” and “The Good, The Bad, The Weird.” His Hollywood directorial debut was in 2013 with “The Last Stand,” featuring Arnold Schwarzenegger.

The film opens in local theaters on Sept. 7.

By Rumy Doo (doo@heraldcorp.com)