The star posed with self portraits by young Cambodians affected by Aids

The all-action star, who has begun a three day tour in Cambodia, is following in the footsteps of fellow actors Roger Moore and Jessica Lange.

"I want to stop the spread of HIV/Aids and protect children who are affected by landmines," he said.

The actor, 50, contacted the UN after seeing a film about land mines.

Rehabilitation centres

"I always think I am so lucky. So, now it's time to give back," he told reporters on his first day in Cambodia.

During his stay, the Rush Hour star will visit children suffering from Aids and tour land mine rehabilitation centres in the region.

In Cambodia, many weapons, including up to 6 million land mines, remain following the Vietnam War and three decades of civil conflict.

He stars opposite Steve Coogan in Around the World in 80 Days

The country also has Southeast Asia's highest HIV infection rate.

'Genuine concern'

On Tuesday, Chan will travel to Siem Reap, home to the country's cultural icon, Angkor Wat, where he is to meet with Buddhist monks helping children and families affected by the HIV virus.

He will also help explosives experts destroy a land mine. "Whatever I can do, wherever I can go. I promise you I'll do it," said the Hong Kong star.

Unicef's Rodney Hatfield added: "We are confident that Jackie's prestige, great talent and genuine concern for children will help the United Nations send a powerful message on the impact of HIV/Aids and conflict on children."

Chan's career in Chinese-language films, and latterly Hollywood, has spanned more than 20 years.

The actor will next be seen in the forthcoming Around the World in 80 Days opposite British comedian Steve Coogan, opening in the UK in July.