The Twin Otter plane with nine passengers and three crew went missing on Friday morning and its wreckage was spotted from the air in a hard-to-reach area on Saturday.
"Looking at the condition of the crashed plane, we can say that all 12 people died in the accident but haven't been able to be evacuated as the weather was bad," Papua police spokesman Kartono Wangsadisastra said on Sunday.
Speaking by phone from the provincial capital Jayapura, 4,000 km (2,500 miles) east of Jakarta, he said evacuation efforts would continue on Monday.
Search-and-rescue helicopters had airlifted three people into the crash area, but a thick haze halted their efforts for the day, rescue official Mardi told Reuters.
On Saturday, Wangsadisastra had said the plane apparently struck a mountain because of smog or (bad) weather.
The plane had reportedly been chartered by a local government body to transport officials. All on board were Indonesians.

Copyright Reuters, 2006