The appeals have come in the form of faxes and emails that flooded Aljazeera website after the airing on Aljazeera television of a videotape showing Japanese hostages captured in Iraq.
On Thursday, the television aired a chilling, soundless tape showing the three hostages sitting at the feet of heavily armed kidnappers.
A previously unknown group called Saraya al-Mujahidiin said it would "burn them alive" if Tokyo did not withdraw its troops from Iraq.
The Japanese messages pointed out that the hostages - Noriaki Imai, Nahoko Takato and Soichiro Koriyama - were in Iraq for humanitarian purposes and had strongly opposed the US war on Iraq and deployment of Japanese forces.
Fukushima Mizuho, the leader of the opposition Social Democratic Party, in a fax said the hostages "love Iraq and Iraqi people". She called for their immediate release.
The Pacific Asia Resource Centre, a Japanese non-government organisation, also sent an appeal to the hostages-takers saying they opposed the occupation of Iraq.
Hundreds gathered outside the
official residence of PM Koizumi
"We want you to know that very large numbers of Japanese people have been strongly opposing the presence of Japanese military forces in your country. However, please remember killing the three innocent Japanese you are now holding hostage will not solve the problem. Instead, it will only create hatred towards your country by our people.
Please be patient and give us more time to convince our government to withdraw from Iraq."
Ueda Fumio, the mayor of Sapporo city where activist Imai comes from, also urged the captors to release all the hostages.
"(Imai) entered Iraq to study on his own the effects of nuclear pollution and depleted uranium shells hoping that he would contribute to peace and stability in Iraq someday. He is a peace-loving young person with strong ambitions," wrote Furnio.
"There is no reason for them to be involved in such a tragic case as this despicable act of violence."
Nahoko Takato was working with
street children in Iraq
Other Japanese also expressed similar distress over the incident. "I understand the anger of the Iraqi people towards our government, which is working as a war dog for the US aggression. But why must a peace activist Imai be punished in place of the prime minister Koizumi and other hawkish sycophants?" wrote Yukiko Maruta.
"These three people are working on aid workers [sic] and a journalist. They went to Iraq not to fight against Iraqi people, destroy Iraq, but they would like to help the people. I do not understand why they have to accept this fate, at all. Please air the news that they are not fighters but aid workers. I can not let them die."
Meanwhile, families of the hostages gathered in Tokyo on Friday to plead for the government to do whatever it takes to bring them safely home, including withdrawing troops from Iraq.
Looking pale and tense, relatives of the three met Foreign Minister Yoriko Kawaguchi.
One young man held Buddhist rosary beads tightly. Others clutched handkerchiefs.
"I can't bear the thought that my child might be burned alive," Koriyama's mother, Kimiko, was quoted by Kyodo news agency as telling a news conference.
"I believe that mothers over there [in Iraq] know best how it feels to lose one's child in war. I hope the Iraqi people too will hear our plea."
Video footage showed the hostages with knives at their throats, although this was not aired in Japan. Takato could be heard screaming as she covered her face.
Soichiro Koriyama is a former
soldier turned photojournalist
Imai's father, Takashi, told the same news conference that they had called on Kawaguchi to consider withdrawing the troops.
"But the foreign minister only said she would pass this on, which was a great pity."
The families also said they wanted to meet Prime Minister Junichiro Koizumi to make their appeal directly.
Asked in parliament if he would meet them, Koizumi said: "At the moment, the foreign ministry is handling this."
For the families it was an anxious day.
"We shouldn't have let him go," Naoko Imai was quoted by the Asahi Shimbun daily as saying of her son.
Imai, 18, graduated from high school last month. He is a member of the Campaign to Abolish Depleted Uranium and travelled to Iraq on 1 April to study the effects of depleted uranium on Iraqi children, according to the Citizens’ Network for DU Abolition. Imai was planning to write a book documenting the stories of victims of depleted uranium. "Mr Imai has been deeply saddened by the fact that many innocent Iraqi children have been suffering from cancer and leukaemia," wrote the organisation in a fax.
Takato, 34, is also an aid worker and peace activist. She travelled to Iraq in April 2003, after US and British tanks entered Baghdad, wrote her friend Tomoatsu Kayano. She spent months there helping hungry street children and drug addicts. Takato also delivered food to hospitals, pencils and notebooks to schools and assisted in the reconstruction of a school. This was her third trip to Iraq.
Freelance photojournalist Koriyama, 32, is a former soldier turned freelance photojournalist. Last May, Koriyami provided the Weekly Asahi magazine, published by the mass-circulation Asahi Shimbun, with pictures of Baghdad after the city fell.