A senior US official pressed Japan to act in the coming months to address concerns by US parents over child abductions, warning of rising anger by lawmakers against the ally.

Japan said in September that it was seriously considering signing the international treaty to stop child abductions, although officials said it may take time as the nation would need to change domestic laws.

"It's going to be important that we see progress soon on this issue. There is a building degree of anxiety -- and in some places anger -- on Capitol Hill," said Kurt Campbell, the assistant secretary of state for East Asia.

Calling himself a "strong supporter" of the alliance with Japan, Campbell asked the country both to sign the Hague treaty and to deal "responsibly and humanely" with pending cases.

"Let's take the opportunity, over the next several months, to get this done and to move beyond this issue and focus on the critical issues between the United States and Japan and a new Asian set of circumstances," Campbell told reporters.

Japan is the only major industrial country that has not signed the 1980 Hague Convention, which requires the return of wrongfully held children to their countries of usual residence.

Japanese courts almost never grant custody to foreign parents, particularly fathers. Activists say that thousands of foreigners, mostly men, have been barred at some point from seeing children taken to Japan by estranged partners.

The US House of Representatives has urged Japan to act "immediately" on child abductions. A September resolution said that 136 children were held in Japan at the time against the will of a US parent.

Conservative Japanese lawmakers have argued that laws are needed to protect women from abuse by foreign men.