The 34-year-old announced his retirement in a letter published by Russian news agency RIA Novosti. 

"In addition to constant knee pains, other injuries have also appeared," he said. 

"It is becoming more and more difficult to keep fit, so I decided that it was time to leave sport."

Ahn was born in South Korea, competing for the country at the Turin 2006 Winter Olympic Games, where he earned three gold medals and a bronze. 

He then fell out with the Korean Skating Union and picked up a knee injury in 2008. 

Both incidents resulted in Ahn being left out of the South Korean team for Vancouver 2010, with the skater subsequently becoming a Russian citizen and joining their team in 2011. 

He achieved another three Olympic gold medals and a bronze at Sochi 2014. 

Ahn was left off the list of Russian athletes eligible to compete at the 2018 Games in Pyeongchang, however. 

The International Olympic Committee banned Russia from Pyeongchang 2018 over "systematic manipulation" of the anti-doping system at Sochi 2014, but left the door open to athletes with no history of doping to compete as neutral athletes.

Ahn was never publicly implicated in a doping case and the IOC did not disclose a specific reason for his exclusion, but mentioned "lingering suspicions" about doping use.

During his career, Ahn also earned six world titles between 2003 and 2014. 

He retired once before, in September 2017, before reversing his decision in an attempt to compete at the Beijing 2022 Winter Olympic Games.