Japanese Prime Minister Junichiro Koizumi has said he will ask the US for "special consideration" for alleged US army deserter Charles Jenkins.
Mr Koizumi wants Washington to be lenient
Mr Jenkins arrived in Tokyo on Sunday for medical treatment, despite the threat of being handed over to the US.
Washington wants to try Mr Jenkins on charges of desertion, after he arrived in North Korea in 1965.
The Japanese public is sympathetic to Mr Jenkins, who is married to a Japanese woman abducted by North Korea.
She was allowed to return to Japan in 2002 with the other abductees. But Mr Jenkins remained in North Korea with the couple's two daughters, fearing he would be sought by the US.
Earlier this month, the family held a dramatic reunion in Indonesia, which does not have an extradition treaty with the US.
But Mr Koizumi has lobbied hard for Mr Jenkins to come to live in Japan.
His wish came true on Sunday, when television footage showed a frail Mr Jenkins using a walking stick as he hesitantly disembarked from the plane to a waiting bus at Tokyo airport.
He was taken to hospital for urgent medical treatment. Reports say he is suffering from a serious stomach condition, for which he has already had surgery in the North Korean capital, Pyongyang.
"If possible, we need to seek special consideration for
him from the United States," the prime minister told reporters on
"We will continue negotiations with the United States while he is under medical treatment," he added.
The US ambassador to Japan, Howard Baker, said on Saturday that the US would consider delaying its request for Japan to turn over Mr Jenkins while he is in hospital.
But on Thursday, a State Department spokesman stressed that Mr Jenkins was not in the clear, and that Washington would pursue Mr Jenkins under a Status of Forces agreement between the the US and Japan.
The former GI has been accused by Washington of four counts of desertion - a charge his family back in America denies.
They maintain he was kidnapped by North Korea like his wife Hitomi Soga.
"We're glad that he's got to Japan where he can get some proper medical treatment," Mr Jenkins' nephew James Hyman told Japan's NTV network.
"He has had a very rough life and we're just glad that he's in a country now where he can live freely," he said.