LIMA, Peru (AP) _ The army said Wednesday it will send helicopters to search an inaccessible stretch of Peru's Amazon jungle for four men, including a Belgian ornithologist, who disappeared while filming a documentary.

The men, who have been missing for 11 days, were preparing a film on the pre-Incan ruins of Gran Pajaten and wildlife in Abiseo River national park, in the province of San Martin, 325 miles north of Lima, the army said.

``If the rain stops and the weather is good, we will send a helicopter with a high-risk rescue group to fly over the area as soon as possible,'' an army spokesman said, speaking on condition of anonymity.

The group's leader, Peruvian documentary filmmaker Alejandro Guerrero, and two Peruvian guides separated from the four men after 28 days in the jungle and returned to Lima. The group disagreed over whether to end the trip or continue exploring a remote swath of virgin jungle to look for new species of birds and animals, Guerrero said.

Four groups members, headed by Belgian ornithologist Jean de Coninck, decided to continue exploring and separated from Guerrero and the guides.

Besides Coninck, who lives in Peru, ornithologist Segundo Rivadeneyra, entomologist Mario Clinton Callegari and Marcial Huaman, all Peruvians, are also lost, the army said.

Guerrero said the four men were carrying only machetes and matches, and lacked food or water.