WASHINGTON (REUTERS) - Unified light heavyweight world titleholder and former Olympic champion Andre Ward announced his retirement from boxing on Thursday.

The 33-year-old American, who is regarded by many as the best pound-for-pound boxer today, attributed both the physical demands of the sport and a waning desire to fight for his decision to leave the sport.

"I want to be clear - I am leaving because my body can no longer put up with the rigours of the sport and therefore my desire to fight is no longer there," Ward said in a statement on his website.

"If I cannot give my family, my team, and the fans everything that I have, then I should no longer be fighting."

Ward, who won the gold medal at the 2004 Olympics, earned a career professional record of 32-0, including 16 wins by knockout.

His most recent fight was in June when he earned an eighth-round stoppage over Sergey Kovalev to retain the three light heavyweight world title belts he won from the Russian in a contentious points decision seven months earlier.