Indonesian investigators are probing the cause of a deadly crash on the Indonesian island of Java that killed at least three people, the country’s prime minister said.

“The cause of the crash remains unknown,” Suharto said at a news conference on Wednesday.

Investigators are searching for a passenger jet that crashed on the island on Wednesday, Indonesia’s prime minster said, adding that he did not know the nationality of the passenger or the plane involved.

The Boeing 777 that crashed was carrying Indonesian President Joko Widodo and his wife, he said.

Indonesia is one of the world’s most heavily armed countries, with about 1,600 soldiers, police, navy and air force personnel.

On Wednesday, a team of investigators were working to determine how the plane, which was travelling from the Indonesian city of Surabaya to the Indonesian capital Jakarta, came to rest in a wooded area, Indonesia news agency Bernama reported.

There were no survivors on the plane.

The cause of death will be formally reported on Friday, Suhartos office said in a statement.