An American tourist has been kidnapped in Uganda's most popular wildlife park by gunmen who demanded a ransom of $500,000.

Kimberley Sue Endecott, 35, from California, and her Ugandan safari guide Jean Paul, 48, were ambushed by four armed men in Queen Elizabeth National Park.

Ugandan security forces were searching for them in an area close to the border with Democratic Republic of Congo.

Polly Namaye, a Ugandan police spokeswoman, said: "The kidnappers, using the victim's phone, have demanded $500,000. Security teams have cut off all exit areas on the border between Uganda and the DRC in search for the victims."

An elderly couple who were also on the trip were not abducted or physically harmed, and managed to raisee the alarm.

Queen Elizabeth National Park runs along the Congolese border and numerous militia groups and armed gangs roam the east of that country.

Tourism is a key industry for Uganda with hundreds of thousands of visitors each year.

Brigadier Richard Karemire, a Ugandan army spokesman, said the kidnapping was "an isolated incident" and that Uganda remains safe for tourists.

He said: "The security agencies, including the military, are working together to ensure the tourist and the driver are freed unharmed."