Kampala, Uganda CNN  — 

An armed gang who kidnapped an American tourist and her driver at gunpoint from a Ugandan national park have made frequent demands for a $500,000 ransom, which will not be paid, Ugandan police said Thursday.

“They (the abductors) continue to use cell phones of the victims to call the lodge they were staying asking for $500,000 ransom, which we will not offer,” Uganda deputy police spokeswoman Polly Namaye said.

Police say they will intensify the hunt for the abductors instead of offering the ransom and have closed borders near where the tourist and her Ugandan driver were seized during an evening game drive on Tuesday at Queen Elizabeth National Park.

“We want to inform the public and all visitors in the country that the joint security teams have cut off all exit areas on the border between Uganda and the DRC in search for the victims,” Namaye said.

Namaye said the police and other security agencies were working with the US Embassy in Kampala, Uganda’s capital, to rescue the hostages who police believe are still within the country.

A US State Department spokesperson said security forces were responding to the incident, but gave no further details.

“We are aware of reports of a US citizen kidnapped in Uganda. Security forces are responding to the incident. We have no further information to offer at this time,” the spokesperson said.

The American citizen was abducted alongside four people, but the other four were freed while the other two were taken from the park, officials said.

Uganda recorded a spike in domestic kidnap cases last year, prompting street protests by activists who said security agencies were not doing enough to protect the citizens

News of this latest kidnapping could affect Uganda’s tourism sector, one of its most significant sources of foreign income.

The country earned US$1.37 billion in 2016 from tourism, according to the Uganda Bureau of Statistics.

CNN’s Hilary McGann and Anna Cardovillis contributed to this story.