At least 12 people were killed after a Costa Rican plane crashed in a mountainous area off popular tourist beach town Punta Islita beach on Sunday, Reuters reported. Officials are yet to determine the cause of the crash, the government said.

Nature Air, a local company operating the aircraft, issued a statement lamenting the accident without specifying the cause. “Regrettably this plane crashed a few minutes after taking off,” Nature Air said.

The casualties include 10 United States citizens and two local pilots. The flight was part of special charter booked for 20 people.