SAN JOSE, Jan. 2 (Xinhua) -- Costa Rican authorities said on Tuesday they were investigating the cause of a small plane crash over the weekend that killed all 12 people on board, including 10 U.S. tourists.

Michael Soto, of the Judicial Investigation Agency (OIJ), told reporters at a press conference that U.S. authorities had offered to help in the investigation, which currently centered on combing the site of the crash for clues as to whether winds or mechanical failure had played a role.

The Cessna 208B, operated by Nature Air, which took off from Costa Rica's Pacific Coast resort of Punta Islita was on its way to the capital San Jose when it crashed early Sunday in a mountainous region of Guanacaste province.

The foreign victims were members of two families and their guide, while the remaining two victims were the Costa Rican pilot and copilot.

Soto said they were in touch with the U.S. embassy in San Jose to get DNA samples from relatives of the victims for purposes of confirming identification.

According to eyewitness accounts published by a U.S. news outlet, the plane nosedived shortly after take-off.