BANGKOK, Thailand (AP) _ A passenger helicopter crashed into a mountain in Laos killing at least 15 people, diplomats said Tuesday.

The helicopter of the national carrier Lao Aviation was traveling on a regular route between Xaysomboune and Xieng Khouang provinces when it crashed Sunday. No foreigners were reported to be aboard.

Laotian authorities believe the crash site is at the side of a remote mountain north of Long Tieng, about 94 miles north of the capital Vientiane but had yet to reach it, diplomats said.

The cause of the crash was not immediately clear. It happened in an area where anti-government ethnic Hmong insurgents, who have stepped up resistance this year, are active.