Four kidnappers ambushed a group of tourists in Uganda on Tuesday while they were driving through a national park during a wildlife expedition. The kidnappers held them at gunpoint, and abducted a 35-year-old American woman and the 48-year-old safari driver.

The four other tourists were unharmed and alerted authorities. The kidnappers later demanded a ransom of $500,000.

In addition to a rescue party of police, military and game rangers are also making strides to locate the woman and the driver.

"A joint operation by the Uganda police, Uganda People's Defence Forces (UPDF) and Uganda Wildlife Authority game wardens is underway to locate and rescue them," government spokesman Ofwono Opondo said in a statement.

A spokesperson for the Uganda police said the police had dispatched "an elite squad from the tourism police to reinforce the security teams at Queen Elizabeth National Park, to actively pursue a group of four unknown gunmen."

Queen Elizabeth National Park, Uganda's most visited national park, is located about 250 miles from the capital Kampala and near the border of the Democratic Republic of the Congo.

Security teams have cut off exit areas on the border between Uganda and the Democratic Republic of Congo. There have been many reports of gangs and militia groups in the region.

In recent years, Uganda has seen a boost in tourism, with 1.32 million visiting the country in 2017.

Tourists walk along the beach at Kiwayu Safari Village resort, north of Lamu
Tourists walk along the beach at Kiwayu Safari Village resort, north of Lamu Reuters