Related Video: Watch Psy's 2004 protest performance
In 2002, the K-Pop sensation smashed a toy US tank at a protest over the American military presence after two South Korean teenagers were hit and killed by an US military vehicle.
In 2004, Psy was part of a controversial performance alongside South Korean rock band N.E.X.T.'s song "Dear American" in response to the US-led invasion of Iraq. The lyrics included: "Kill those f---ing Yankees who have been torturing Iraqi captives" and "Kill them all slowly and painfully."
On Saturday, Psy apologised ahead of his scheduled Christmas in Washington performance at which US President Barack Obama was set to perform.
"I will forever be sorry for any pain I have caused by those words," the 34-year-old singer said, calling the performance part of a "deeply emotional reaction" to both the Iraq invasion and the death of the two school girls that was "part of the overall anti-war sentiment shared by others around the world."
"While I'm grateful for the freedom to express one's self, I've learned there are limits to what language is appropriate and I'm deeply sorry for how these lyrics could be interpreted."
The singer was confirmed following the release of the statement to still perform at TNT's Christmas in Washington show, with President Obama in attendance.
Psy recently toppped Justin Bieber's "Baby" to have the most watched video on Youtube of all time with "Gangnam Style". The video took just four months to rack up over 920 million hits.
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