The abduction of three Japanese in Iraq plunged Prime Minister Junichiro Koizumi (search) into his deepest crisis since taking office three years ago, as relatives of the hostages and thousands of protesters pressed the government Friday to withdraw Japanese troops from Iraq.

Ruling party officials vowed not to give in to terrorists and reiterated that Japanese soldiers would continue their humanitarian mission in Iraq. Koizumi denounced as "cowardly" the Iraqi captors' threat to burn the three civilian hostages alive unless Tokyo gives in.

Thousands massed near the prime minister's official residence and held a candlelight vigil for captive aid workers Noriaki Imai, 18, and Nahoko Takato, 34; and photojournalist Soichiro Koriyama, 32.

"As a parent, it would be just unbearable to see my child being burned alive, if that really happens," Koriyama's mother Kimiko said at a news conference.

"Time is running out," said Ayako Inoue, Takato's younger sister. "My uneasiness and anxiety grows as the time passes."

In a video obtained by Associated Press Television News, four masked men threaten the blindfolded captives with guns and knives. The Arab TV network Al-Jazeera (search) also received the video and said it was accompanied by a statement saying the hostages would be burned alive if Japan's troops were not pulled from Iraq within three days.

Koizumi pushed forward with the deployment of 1,100 troops to Iraq this year despite deep public reservations about sending Japanese soldiers to a combat zone for the first time since World War II.

Critics said dispatching troops to Iraq violated Japan's pacifist constitution, which bans the use of force to resolve disputes. Many Japanese also said they feared the troops could come under attack and suffer casualties, something Japan's military has not experienced since 1945.

Nearly 2,000 people turned out for the candlelight vigil in the heart of Tokyo's political district, shouting "Defense troops, withdraw right now!"

Three thousand more activists demonstrated at nearby Hibiya park.

Opposition leaders said they want to help Koizumi bring the captives home safely, but would hold him liable for the outcome.

"We foresaw trouble like this when the government decided to send troops to Iraq," said Katsuya Okada, secretary-general of the Democratic Party. "Prime Minister Koizumi bears a serious responsibility for inviting a situation like this."

Tokyo's stock average declined amid worries the crisis could destabilize Koizumi's leadership.

"If you're willing to assume something bad happens, then the public will be very upset and Koizumi and the ruling Liberal Democratic Party (search) will be exceptionally vulnerable," said John Richards, Japan Strategist at Barclays Capital. "Just the feel of that is bad for stocks."

Koizumi called an emergency meeting of his Cabinet and created a task force to formulate a response to the kidnappings. Vice President Dick Cheney visits this weekend, and the prime minister is expected to make a strong request for help.

To protect against further kidnappings, the government has started preparing for the possible evacuation by C-130 military transport plane of some 70 Japanese believed to be in Iraq, Kyodo News agency reported.

Twenty-one Japanese journalists and their support staff have sought refuge in the Japanese military compound in southern Iraq. The troops have offered to transport them to Kuwait.

"We cannot give in to the cowardly threats of terrorists," Koizumi said. But he added: "We don't know who this group is. Right now what we need to do is gather accurate information and bring them [the hostages] home safely."

The government has had no contact with the hostage-takers. Chief Cabinet Secretary Yasuo Fukuda (search) stressed that going along with the withdrawal demand was not under consideration.

Many Japanese voiced support for Koizumi.

"Japan should not give in to this kind of terrorism," said Koichi Yoshida, a 43-year-old executive in Tokyo. "Japan has international responsibilities and national interests that are served by the military's presence there."

Jiro Yamaguchi, a political science professor at Hokkaido University, said the public now supports Koizumi's tough stand. But he said public opinion could be swayed by what happens.

"If Koizumi missteps, he will lose his grip on power," Yamaguchi said. "It all depends on what happens to public emotion."