A decapitated body wrapped in an American flag and found in an insurgent-controlled section of Baghdad was that of a Japanese man kidnapped by Islamic militants, a Japanese official said Sunday.

Foreign Minister Nobutaka Machimura said in Tokyo that the government confirmed that the body found Saturday was that of Shosei Koda (search), 24.

An Al Qaeda-linked group led by Jordanian terrorist Abu Musab al-Zarqawi (search) showed Koda, a backpacker, on a video posted on a militant Web site Tuesday.

The group vowed to behead Koda within 48 hours unless Japan withdrew its troops from Iraq. Prime Minister Junichiro Koizumi (search) quickly rejected that demand, saying he would not give in to terrorists.

Japanese Embassy officials in Baghdad sent fingerprints of the body to the Foreign Ministry in Tokyo, and police experts there positively identified the body as Koda's, Machimura said.

"It is to our great sorrow that after putting all our efforts into securing his release he has become a victim of terrorism," Machimura said.

"We cannot allow this kind of action. Japan, in cooperation with the international community ..., must continue the battle against terrorism."