A helicopter carrying four Americans crashed in Kenya, killing them and the pilot, the Kenyan police said on Monday.

The National Police Service said in a Twitter thread that the helicopter crashed on Sunday evening in Central Island National Park, near the country’s northern border with Ethiopia. It said the cause of the crash had not yet been established.

United States officials confirmed the Americans’ deaths and provided the names of three of the victims — Anders Asher Jesiah Burke, Brandon Howe Stapper and Kyle John Forti Brandon Howe Stapper — to The Associated Press on Monday.

The police service said the helicopter was one of two that had landed at a “tented camp” on the island, and that the other one had cleared the area safely. The Kenyan news outlet Capital FM Kenya reported early on Monday that the Americans were tourists who had visited the camp and were flying out when the crash occurred.

Capital FM Kenya identified the pilot as Mario Magonga and said that he had been among the pilots working for Kenya’s deputy president, William Ruto.

Central Island National Park sits on an island in Lake Turkana, which the Kenya Wildlife Service says is the world’s largest permanent desert lake. The park is less than two square miles in size, and the lake is a three-day drive from the Kenyan capital, Nairobi.

Central Island has three active volcanoes and three crater lakes that provide a habitat for the world’s largest concentration of Nile crocodiles, according to the wildlife service.

Most visitors travel there by air.