Japanese leaders on Sunday insisted they would not cut short their troops' deployment in Iraq despite the discovery of the body of a Japanese backpacker killed by Islamic militants.

Fingerprint tests proved the headless body found in central Baghdad was Shosei Koda (search), 24, who had been held by al-Qaida-linked militants demanding that Japan withdraw its 500 troops from Iraq, said Foreign Minister Nobutaka Machimura.

Prime Minister Junichiro Koizumi (search) called the killing a "brutal, inhuman act" but vowed to stay the course in Iraq, where Japanese soldiers are on a humanitarian, non-combat mission.

"We cannot lose to terrorism, we must not yield to brute force. I believe we should continue to support the Iraqi people's efforts to rebuild their country," Koizumi told reporters.

The United States denounced the killing and commended Tokyo for not bowing to terrorism.

"There is no justification for acts like this," U.S. Ambassador to Japan Howard H. Baker Jr. said in a statement. "We strongly support the Government of Japan's rejection of terrorist demands and deeply appreciate its steadfast commitment."

The killing came despite frantic diplomatic efforts by Japan to rally assistance from the United States and other nations to win Koda's release.

Vice Foreign Minister Shuzen Tanigawa, speaking in Jordan where he had been dispatched as an envoy, said the body would be sent back to Japan through Kuwait.

In a video posted on a militant Web site Tuesday, a group led by Abu Musab al-Zarqawi vowed to behead Koda within 48 hours unless Japan withdrew its troops from Iraq. Koizumi quickly rejected that demand, saying he would not give in to terrorists. As of midday Sunday, the group had not made any claims of responsibility for Koda's death.

The death was the first of a Japanese hostage in Iraq. Five Japanese civilians were taken hostage there in April but were released unharmed. Two diplomats and two journalists have also been killed in separate ambushes, but their deaths were not seen as related directly to the dispatch.

Koda's death could weaken Koizumi's pro-U.S. Iraq policy. The deployment of the troops is set to expire Dec. 14. It will have to be extended for the troops to stay.

The government has not made a public statement on its intention to extend the mission, and officials said on Sunday that the issue was still to be decided. Koizumi said Koda's murder and the extension of the dispatch were separate issues.

"It's a fact that if Japan had not dispatched troops, this incident would not have happened. I will strongly push ... so that it is not extended and the troops are withdrawn," said Katsuya Okada, leader of Japan's largest opposition Democratic Party.

Iraqi officials found Koda's decapitated body in Baghdad on Saturday. Associated Press Television News videotape showed the severed head with the hostage's long black hair and features. Policeman Yassin Hashim, who examined the body, said it was wrapped in an American flag, but Japanese officials did not confirm that.

The ordeal has been excruciating for Koda's family. The family repeatedly appealed on Arabic TV and through international media to the captors, saying their son had no political intentions in Iraq and was simply curious.

"We thank everyone for their trouble. We pray that the Iraqi people will find peace," the family said in a statement released to Nogata city officials.

Koda, who left Japan in January for a yearlong trip starting in New Zealand, had told people he met traveling that he wanted to go to Iraq to see the country. The Japanese Foreign Ministry said Koda entered Iraq on Oct. 21 and was last seen two days later at a Baghdad bus terminal, where he tried to catch a bus back to Jordan.