Photo: WENN.com

'Gangnam Style' may seem like nothing more than harmless pop fun, but an earlier track from Psy's career has caused outrage for its fiercely anti-American lyrics.

The star has enjoyed huge international success in 2012, scoring a Top Ten hit in America with his breakthrough k-pop track (which was even covered on Glee), but early footage of the star has revealed he was once involved in an aggressive protest track against America's involvement in the Iraq war.

The track has surfaced just two weeks before Psy is scheduled to perform in front of Barack Obama at a Christmas In Washington celebration show.

Eight years ago, Psy performed a track with a South Korean metal band, singing lyrics such as: "Kill those f---ing Yankees who have been torturing Iraqi captives' / 'Kill those f---ing Yankees who ordered them to torture / Kill their daughters, mothers, daughters-in-law and fathers / Kill them all slowly and painfully."

Video footage also shows Psy smashing a model of an American tank on stage in protest against an incident in which two Korean schoolgirls were killed by an armoured US vehicle.

Psy has since apologised for the tank incident, saying it was 'part of a deeply emotional reaction to the war in Iraq and the killing of two Korean schoolgirls.'

Psy is greeted in London by press and fans

The star has been widely celebrated in 2012, even addressed Oxford Student union, performed on stage with Madonna and being touted for a duet with Canadian teen star Justin Bieber.

His 'Gangnam Style' video has also been named the most watched video in YouTube history.

See footage of Psy's protest below.

Photos: Psy perfoms 'Gangnam Style' on Australian TV