WASHINGTON - Nearly one-quarter of the US Senate asked President Barack Obama on Monday to press Japan on his upcoming visit about parental abductions, saying Tokyo's policies were an anomaly among developed nations.

Japanese courts virtually never award child custody to divorced foreign parents -- sometimes even handing them to a child's Japanese grandparents instead of giving them to a foreigner.

Activists say that thousands of foreign parents have lost access to children in Japan. The row recently was thrown in the spotlight after a US man was briefly jailed for snatching his own children on their way to school.

In a letter to Obama, 22 senators from both parties said they were troubled that Japan was the only nation among the Group of Seven industrialized nations that has not signed the 1980 Hague Convention that requires countries to return a child wrongfully kept there to their country of habitual residence.

"While we acknowledge that Japan's accession to the Hague Convention is an important goal, the United States must also work with Japan to establish a bilateral mechanism to assist with the resolution of current cases," they wrote.

"We urge you to ensure that the United States continues to raise this issue at the highest possible levels in the context of our close bilateral relationship with Japan," the letter said.

The letter was led by Jim Webb, who heads the Senate subcommittee on East Asia, and signed by both senators from Tennessee, the home state of Christopher Savoie who was jailed in the high-profile child abduction case.

The letter voiced hope that Japan's new Prime Minister Yukio Hatoyama would do more to address the issue, which was also raised last month in Tokyo by the ambassadors of the United States and seven other Western nations.

Obama is set to visit Japan this week on the start of a four-nation trip to Asia.

Hatoyama's center-left Democratic Party of Japan in August ended a half-century of nearly uninterrupted conservative rule.

Hatoyama has pledged to build a less subservient relationship with the United States and is expected to raise with Obama a row over US bases in Japan.