Japan says it will not bow to the demands of Islamic militants in Iraq who are threatening to execute a Japanese man if Tokyo does not withdraw its troops.

A government spokesman told reporters Prime Minister Junichiro Koizumi established a crisis center shortly after a video was posted on the Internet late Tuesday, showing a Japanese man being held hostage.

The militants identified themselves as members of a group calling itself al-Qaida in Iraq and led by wanted terrorist Abu Musab al-Zarqawi. They threatened to kill their captive if Japanese troops are not pulled out within 48 hours.

Relatives of the hostage in the southern Japan (Fukuoka) identified him as 24-year-old Shosei Koda. They said he traveled to New Zealand earlier this year, but since then his whereabouts had been unknown.

Militants in Iraq kidnapped five Japanese citizens in April and made similar demands before eventually releasing them.