Afghan police freed a kidnapped Japanese aid worker in a raid, hours after he was seized by a group of gunmen, an official said.

"He is freed and is fine," Interior Ministry spokesman Zemarai Bashary said in Kabul.

Bashary said one of the kidnappers was wounded in the encounter with police in eastern Nangrahar province, from where the Japanese man was seized while working on a construction site.

He said the identity of the abductors was not immediately clear. Earlier, a provincial official said police had freed the man's local driver.

Taliban insurgents, who have been behind a series of abduction of Afghans and foreigners in recent years, said they had no information about the incident.

Earlier, the Japanese government said it was looking into the kidnapping of the man, identified as 31-year-old Kazuya Ito, who worked for a non-governmental organisation called Peshawar-kai.

Ito's mother told reporters her son had wanted to work in Afghanistan, even at the risk of his own life.

"He said he was having fun, that he was getting along with others," she said.

Japan does not have troops in Afghanistan, but its navy runs a maritime refuelling operation in support of US-led military operations in the country.

Asked how the abduction would affect Japan's naval mission in Afghanistan, a foreign ministry spokesman said only that the incident was an example of the conditions that required international efforts to help reconstruct the country.

The refuelling mission is set to become a focal point of a session of parliament to be convened next month.

Unpopular Prime Minister Yasuo Fukuda wants to extend the mission in the Indian Ocean after legislation expires in January.

But the opposition-controlled upper house will almost certainly reject a new bill to do so and the junior partner in the ruling coalition is wary of upsetting voters, many of whom oppose prolonging the mission, by forcing through the bill.

Peshawar-kai, based in southern Japan, was set up in 1983 and provides medical services in Pakistan and Afghanistan, according to its website.