US Vice President Dick Cheney has given strong support to the position taken by Japan towards the kidnappers of three Japanese citizens in Iraq.
Relatives of the hostages have pleaded for the government to help
Japanese Prime Minister Junichiro Koizumi has rejected the kidnappers' demands to withdraw Japanese peacekeepers from Iraq.
During a visit to Tokyo, Mr Cheney promised that Washington would do everything it could to help.
Some Japanese newspapers believe it is the worst crisis Mr Koizumi has faced.
A mass-market Japanese tabloid has condemned the prime minister's close relationship with the US administration in a front-page photo spread.
Gendai published a photo of a laughing Mr Koizumi with President Bush's hand on his shoulder next to shots of grieving relatives of the hostages in its Monday edition, and accused the government of panic and incompetence.
If it reflects the popular mood, Mr Koizumi is indeed in trouble, the BBC's Jonathan Head reports from Tokyo.
'Help my son'
The deployment of non-combat troops to Iraq has been highly controversial in Japan which has not sent soldiers to combat zones for decades, in line with its pacifist constitution.
JAPANESE IN IRAQ
550 troops are in the south-eastern city of Samawah
The soldiers are tasked with rebuilding infrastructure
It is Japan's first post-war deployment to a combat zone
There were reports that the three would be freed on Sunday but the day passed with no release, and their fate is now unknown.
With little news emerging, the distraught relatives have made further pleas to the Japanese government to act to save them.
"What we want most of all is for the troops to be withdrawn to save their lives," Ayako Inoue, sister of aid worker Nahoko Takato told Reuters.
Ms Takato, 34, is being held together with Noriaki Imai, 18, who was in Iraq to research the effects of depleted uranium weapons and 32-year-old photojournalist Soichiro Koriyama.
"We thought we would see the cheerful face of my son by noon, but we have not received any confirmation yet," Mr Koriyama's mother Kimiko said, a reference to reports that the hostages would be freed by Sunday lunchtime, Japanese time.
"Please help my son."
Chief Cabinet Secretary Yasuo Fukuda has warned there is no longer any certainty of a favourable end to the crisis.
People in Tokyo react to the hostage crisis
"At one point we were able to make the judgment from
various perspectives that they were safe, but now that's
unconfirmed," he said.
Video footage last Thursday showing the three hostages blindfolded and with a gun to their heads stunned the Japanese people.
Correspondents say that in safe and orderly Japan the kidnappings have been a source of nationwide anguish.
However, a fresh contingent of troops left for the Gulf on Monday.
About 25 Air Self-Defence Force members left Komaki air base in Aichi Prefecture for Kuwait in the second personnel rotation since Japan started its Iraqi deployment in December.