A body found in Iraq is unlikely to be that of Japanese hostage Shosei Koda, Japanese officials say.
Militants demanded Japan withdraw its troops
Medical officers who had examined the body said its dental structure did not match that of the missing 24-year-old.
The body was found between Baghdad and Tikrit, coinciding with the expiry of a 48-hour deadline set by his kidnappers.
Islamic militants led by Abu Musab al-Zarqawi had threatened to behead Mr Koda if Tokyo did not pull troops out of Iraq by Friday.
Government officials announced earlier on Friday
that a body had been found that resembled Mr Koda.
It was sent to medical experts for positive identification in Kuwait.
"The medical officers at the embassy in Kuwait
examined the body and they concluded that it is not likely that it is the remains of Mr Koda," Chief Cabinet Secretary Hiroyuki Hosoda said, the AFP news agency reported.
"His dental structure is completely different," he added.
In a video released onto the internet, militants claiming loyalty to Abu Musab al-Zarqawi threatened to behead Mr Koda within 48 hours if their demands were not met.
Earlier this year Japan managed to free five other citizens taken hostage in Iraq after days of mediation.
Mr Koda's family appealed for his release
Mr Koda, from Nogata, in Japan's Fukuoka prefecture, left on a year-long trip in January, starting in New Zealand.
He told people he met on the way that he wanted to go to Iraq to see the country.
Officials said he took a bus to Baghdad from Amman in Jordan last week, and was seen up until last Sunday attempting in vain to find accommodation in the city.
On Friday his family issued an appeal for his release.
His brother Maki said: "My brother is just a civilian. He is a young man who saw that the people of Iraq were suffering and left on his journey with the wish to help them.
"So, please let him return to Japan safely. Once he returns, he will become a man who will work for Iraq and world peace. So please, let him return alive."
Japan has about 550 non-combat troops in Iraq. They are mainly engaged in humanitarian and reconstruction work.