Japan's military on Wednesday joined the search for a seven-year-old boy missing in the country's north since his parents said they abandoned him in a bear-inhabited mountain forest, officials said.
A total of 75 personnel from the Ground Self-Defence Force -- Japan's army -- joined some 130 fire rescuers, police officers and volunteers to look for the boy, rescuer Satoshi Saito told AFP by telephone.
Yamato Tanooka has been missing since Saturday after his parents said they made him get out their car on a mountain road as punishment for misbehaving. He is reportedly without food or water.
Rescuers have admitted it is a frustratingly difficult task to find the vanished boy due to a lack of evidence found so far of his presence in the rugged mountainous area on the wild bear-inhabited island of Hokkaido.
The boy's parents originally told police their son had got lost while they were out hiking to gather wild vegetables -- but later admitted they were angry and tried to punish him because he had thrown stones at cars and people.
The local town of Nanae requested military support after rescuers and police officers had already scoured the area for four days, with heavy rains at times hampering the search.
"We asked the SDF to go into places which people can't easily access such as deep crevasses along creeks," town spokesman Mitsuru Wakayama told AFP.
"We have already covered the same areas over and over again," he said, but added that it is hard to imagine even a lost adult being able to travel over such an extensive area on foot.
"We have not taken such a long time before to find signs of a person in distress," he said.
The parents told police they abandoned Yamato on a road, bounded on both sides by thick mountain forests, but quickly returned to find him missing.
On the northern side of the road where the boy is believed to have been abandoned is a slope of Mount Komagadake, which rises to an altitude of 1,131 metres.
"The military personnel will scour the mountain slope," said Saito, the rescuer.
"Unless he started climbing the mountain, he would have hit a main road after walking for two-three kilometres in any other direction," Saito said earlier.