"Since our Self-Defence Forces are providing reconstruction support for Iraqi people, we have no reason for withdrawal," Chief Cabinet Secretary Yasuo Fukuda told a news conference.

Earlier a previously unknown group, calling itself the "Mujahedeen Brigades," threatened to kill three Japanese nationals it said it had abducted unless Tokyo withdrew its troops from Iraq, in a videotape aired by the Al-Jazeera satellite channel.

The Qatar-based television aired soundless video of the trio and their passports, adding that an accompanying statement had given Tokyo three days to meet the group's demands.

The three appeared blindfolded in parts of the video, while other shots clearly showed their faces and the rest of their bodies.

The government and news reports identified the three as Noriaki Imai, a 18-year-old male volunteer worker, Nahoko Takato, 34, a female volunteer worker, and Soichiro Koriyama, a 32-year-old male freelance photojournalist.

But Fukuda said the government had still to confirm they had been kidnapped.

"The government is doing our best to gather information," he said. "If innocent civilians are taken hostage as reported, it is unforgivable and I feel strong resentment. We demand their immediate release."

Fukuda said however Tokyo had not received any demands directly from the apparent kidnappers.

"We have not made any contact with the group yet," he said, adding the government would send a senior foreign ministry official to Jordan on Friday to handle the case.

Japan, a close ally of the United States, has deployed some 550 ground troops to Samawa in predominantly Shiite southern Iraq as part of the US-led coalition's humanitarian work, despite strong objections at home.

Japanese soldiers have been tasked with providing clean water, medical assistance and helping repair public facilities in Samawa.

Foreign Minister Yoriko Kawaguchi said if the reports were true it would be "extremely regrettable" given Japan's efforts to help with Iraqi reconstruction.

Fukuda defended the government's decision to send troops to Iraq.

"Doesn't terrorism occur if we do not send the Self-Defence Forces?" Fukuda said when asked about the government's responsibility for the deployment and the reported abductions.

"Terrorism can occur anywhere," he said, adding that rescuing the hostages was more important than debating the dispatch of Japanese troops.

The military deployment is Japan's first since World War II to a country where fighting is ongoing and has caused controversy because of the risk of being drawn into combat, potentially violating the nation's post-war pacifist constitution, which bans the use of force in settling international disputes.

Kawaguchi repeated a government advisory that Japanese nationals, including reporters, evacuate from Iraq as soon as possible.

"An evacuation recommendation has been issued in Iraq, but I want to say again that I strongly urge Japanese nationals to leave Iraq as soon as possible," Kawaguchi said.

Seven South Koreans, described as church pastors were also seized by armed insurgents in Iraq Thursday, foreign ministry officials in Seoul said.

They were seized driving on a main highway linking Baghdad with the Jordanian border, officials said.

WAR.WIRE