Ugandan security forces scoured dense bush on Thursday in the hunt for a US tourist and her safari guide who were kidnapped by gunmen in the country’s most popular national park.
"The operation to rescue the tourist is still ongoing," Uganda's tourism minister, Godfrey Kiwanda, said on Thursday.
Four kidnappers stopped a group of tourists at gunpoint around dusk on Tuesday as they drove through the Queen Elizabeth National Park on safari to see wild animals.
Police identified the American as a 35-year-old Kimbley Sue Endecott and said the kidnappers had used her mobile telephone to demand a ransom of $500,000 (445,000 euros) for the release of the pair. The driver is Jean Paul, a 48-year-old safari guide with years of experience.
Police spokeswoman Polly Namaye said all efforts were being made, adding that Uganda's top-ranking police officer, Inspector General of Police Martin Okoth Ochola, had flown to the area to lead operations.
"The operation is continuing," she said.
The gunmen dragged the pair from their safari vehicle, but left behind two other tourists, whom police described as an "elderly couple". They managed to raise the alarm from the lodge where they were staying.
Army spokesman Brigadier Richard Karemire said the security forces were doing all they could to track down the gunmen.
"Let the security forces do their work," he said Thursday.
There was much speculation but no information as to who the gunmen behind the attack might be.
The US embassy in Kampala said it was aware of the kidnapping, warning its citizens to "exercise caution when travelling to this area due to ongoing security activity."
Soldiers have fanned out along the porous border with the Democratic Republic of Congo, with security forces insisting they believe the pair remain in the country.
The Ugandan police's tourist protection force has also deployed a special response unit working alongside soldiers and wildlife rangers.
Queen Elizabeth National Park, one of the East African nation's most popular wildlife reserves, runs along the frontier with conflict-wracked regions of DR Congo. It borders on the famous Virunga national park, the oldest in Africa.
Numerous militia groups and armed gangs roam eastern DR Congo. Virunga suspended all tourism activities last year after a ranger was killed and two British tourists kidnapped.
The Britons and their driver were freed two days after the attack. The park reopened in February.
The Ugandan park straddles the equator, covering 1,978 square kilometres (764 square miles) in the country's southwest region.
Queen Elizabeth park is about 150 kilometres (90 miles) north of Bwindi Impenetrable National Park, famous for gorilla trekking. Uganda is home to more than half of the world's endangered mountain gorillas.
In 1999, Rwandan rebels killed eight foreign tourists and four Ugandans there, inflicting an enormous blow to Uganda's tourist industry. The rebels were part of a militia group that was involved in the 1994 Rwandan genocide before fleeing to the jungles of DR Congo.
Tourism is a key industry for Uganda, as a major earner of foreign currency. Hundreds of thousands of tourists visit each year.