Bollywood actors Hrithik Roshan and Katrina Kaif are leaving no stone unturned to impress the audience in their upcoming action thriller, "Bang Bang".

According to reports, both Hrithik and Katrina are undergoing arduous workout sessions for "Bang Bang" in which they are expected to give out high voltage action stunts.

"Hrithik has been spending a lot of time working on his body. Katrina too has taken up strenuous workout sessions. The movie is an action-thriller, so they both have to look the part," a source told Hindustan Times.

"Initially, they were supposed to shoot in Kashmir but the production house did not get the necessary permissions. As they couldn't wait any longer (due to Hrithik and Katrina's tight schedules), they changed the location to Europe", the source added.

Hrithik and Katrina have reportedly wrapped up the shooting of "Bang Bang" in Thailand and would be off to Greece for the next schedule.

Katrina, who has another action movie "Dhoom 3" in her kitty, has reportedly decided to undergo significant changes in her appearance for "Bang Bang". She has decided to get tanned for the film to make a difference in her looks from Aamir Khan starrer "Dhoom 3".

"The first thing Katrina did to ensure that the two films don't look similar was to change her own look. In Bang Bang she is tanned, looking several shades darker than her usual self," an insider told ANI.

Directed by Siddharth Raj Anand, "Bang Bang" is said to be the Hindi remake of Hollywood movie, "Knight and Day" starring Tom Cruise and Cameron Diaz. The movie, that marks the reunion of Hrithik and Katrina on screen after "Zindagi Milegi Na Dobara", is slated for release on 1 May 2014.