Britain's Prince Harry appealed on Monday for British and US veterans of the Afghan and Iraq conflicts not to be forgotten as he accepted a coveted humanitarian award from a Washington think tank.

Henry, 27, received the Distinguished Humanitarian Leadership Award from the Atlantic Council -- "with great humility," he said -- in recognition of the foundation he oversees with his brother Prince William that helps rehabilitate wounded servicemen and women and reintegrate veterans into civilian life.

"They have paid a terrible price to keep us safe and free," the prince, a British army captain who served in Afghanistan four years ago, told the exclusive black-tie gathering of Washington movers and shakers.

But with foreign forces withdrawing and media attention waning, he said, they were liable to be no longer in the minds of the general public.

"The very least we owe them is to make sure that they and their brave families have everything they need through their darkest days -- and, in time, regain the hope and confidence to flourish again," he said.

"For these selfless people, it is after the guns have fallen silent, the din of battle quietened, that the real fight begins -- a fight that may last for the rest of their lives."

Harry's appearance at the gala fund-raiser overshadowed the evening's principal guest, UN Secretary General Ban Ki-moon, who the Atlantic Council saluted with its Distinguished International Leadership Award.

On the eve of a UN Security Council meeting on Syria, Ban once again condemned the 'brutality' of President Bashar al-Assad's forces, but added that attacks by opposition groups have also 'escalated'.

"We are in a race against time to prevent full-scale civil war -- death on a potentially massive scale," Ban said. The UN already estimates that well over 9,000 people have died in the 14-month old uprising against Assad.

Others honored Monday included Unilever chief executive Paul Polman, German violinist Anne-Marie Mutter -- who performed George Gershwin's aria 'Summertime' -- and all 1.5 million enlistees in the US armed forces.

It was Harry's first ever visit to the US capital, where he failed to acknowledged a small bevy of mainly female wellwishers when his limousine pulled up to the luxury Ritz Carleton hotel for the gala.

Earlier in the day, he mingled with 125 guest at the British embassy, many of them US and British military personnel who took part in the Warrior Games, a competitive event for war wounded, in Colorado last week.

He also planted a tree in honor of his grandmother Queen Elizabeth II's six decades on the throne.

Through a foundation in their name, the princes -- building on the humanitarian reputation of their late mother Princess Diana -- tackle the issue of caring for disabled and wounded servicemen and women.

His laurel from the Atlantic Council is the same one the think tank -- celebrating its 50th anniversary -- presented to Irish rock star and development activist Bono two years ago.

Harry recently completed 18 months of training as an Apache attack helicopter pilot and has expressed a determination to return to Afghanistan. He was hastily withdrawn from his first tour of duty in 2008 when a media blackout was broken.

Harry made his first solo overseas tour in March, representing Queen Elizabeth in her diamond jubilee year in the Caribbean and Brazil. Royal watchers said it helped the hard-partying prince reshape his public image.