Rescuers spotted the wreckage of an Indonesian military plane that crashed into a jungle-clad mountain with 18 people on board, including three foreigners, but were unable to reach the site Friday, the deputy chief of the air force said.

The condition of the five crew and 13 passengers was not immediately known, said I Gusti Made Oka.

The 1984 Casa-212 plane disappeared during an aerial surveillance mission Thursday about 60 miles south of the capital, Jakarta.

An Indian, a Singaporean and a Briton working for the Singapore-based company Credent Technology were on board testing new camera equipment, said air force spokesman Chaeruddin Ray.

Hundreds of police and soldiers combed the dense jungles Friday, while members of the air force took to the skies, spotting the plane's wreckage just before nightfall on the mountain's steep, rugged slopes.

"They were unable to get close or to land because darkness was already falling," said Oka. "We will not be able to say anything about the condition of the passengers or crew until our rescue teams reach the scene."

Medical teams were on standby for possible evacuations, he said.

Indonesia has seen a spate of airline accidents in recent years. It was the second incident involving a Casa-212 plane in 2008, after a flight operated by the private Dirgantara Air Service crashed in January with three people on board.