SANAA, Nov 18 (AFP) - A Japanese engineer kidnapped near Sanaa is still being held by Yemeni tribesmen, a mediator said on Wednesday, while Japan's prime minister expressed hope the 63-year-old's release was "close."

Sheikh Abdul Jalil, a tribal leader in Arhab, northeast of Sanaa where the engineer was kidnapped on Sunday, announced late Tuesday that the engineer -- identified in Japanese media as Takeo Mashimo, 63 -- was free.

On Tuesday, however, he backtracked, admitting the announcement had been a "mistake."

"The abductors had said they would free the hostage and had left to get him but when they came back they said they had changed their mind," said Sheikh Jalil.

According to him, the abductors had agreed to release the hostage in exchange of the release of their relative, who is being detained by police, within 15 days.

"But at the last minute, they came back saying they want him liberated in three days," the sheikh said.

The kidnappers were distrustful because a previous promise by President Ali Abdullah Saleh to release a detainee was not fulfilled, according to sources close to the kidnappers.

Japan's Prime Minister Yukio Hatoyama, meanwhile, said in Tokyo Wednesday that he was hopeful the hostage would be released soon.

"We are in a situation where he is not yet completely free," Hatoyama said.

However, he added: "I am growing more hopeful that the release is close."

Hatoyama said there was no sign the engineer -- an employee of a Tokyo-based consultancy working on a project to build an elementary school funded by the Japan International Cooperation Agency (JICA) -- had been harmed in captivity.

The engineer was abducted on Sunday in the Arhab region, northeast of the capital Sanaa, with the kidnappers demanding he be exchanged with a detained tribesman.

The 22-year-old tribesman was imprisoned by US forces for a year in Iraq, said a source in Yemen.

He was later arrested in Syria before being held in Sanaa, where he was sentenced to two years in prison without charges, the same source said.

Many Yemenis who lived in Iraq returned home after the 2003 US-led invasion that toppled the regime of late dictator Saddam Hussein.

Yemeni tribes habitually kidnap foreigners to try to put pressure on local authorities. More than 200 foreigners have been seized during the past 15 years, with most being freed unharmed.

But five Germans and a Briton who were taken captive in June in the north of the country are still missing with no word on their fate.

They were among nine people seized in the northern Saada region, the stronghold of Shiite rebels led by Abdel Malek al-Huthi. The three others in the group -- two Germans and a South Korean -- were killed.

Two Japanese women were released unharmed in May last year after briefly being taken hostage by Yemeni tribesmen. (By Hammoud Mounassar/ AFP)