TOKYO: Foreign Minister Katsuya Okada pushed Sunday for a speedy Japanese review of a US base realignment plan, showing widening differences with the prime minister, who wishes to spend more time on the issue.

"We must reach a decision as the cabinet" of Prime Minister Yukio Hatoyama, Okada said during a visit to southern Okinawa island, which reluctantly hosts more than half of the 47,000 US troops in Japan.

"We cannot put it off that long," said Okada, who is under strong pressure from Washington and many Japanese experts to implement the existing plan.

Hatoyama, who came to power in September, has rattled Washington by saying he is reviewing the 2006 agreement to close one base on Okinawa and build a replacement facility in a less populated area of the island.

The premier has maintained that Japan may instead push for moving the base off the island, perhaps even out of the country, to lighten the burden on Okinawa residents, who have long complained of the heavy US military presence.

Hatoyama, in Singapore for a summit of Asian-Pacific leaders, told Japanese reporters Saturday that he had not promised US President Barack Obama that he would reach a conclusion by the end of this year.

Defying US pressure to stick with the pact, Hatoyama, who met Obama on Friday, also said that the review would not be necessary if the existing plan was to be implemented as it is.

Opposition lawmaker Shigeru Ishiba, a former defence minister, called Hatoyama's remark "a breach of trust" of the United States.

Okada attempted to calm the waters and said the review was meant for analysis of the agreement, not necessarily changing it.

He stressed that the review should be concluded before or around the end of this year.

Akihisa Nagashima, vice minister of defence, also separately said Japan must conclude the review soon to allow the US Congress to fund the base relocation plan.

Hatoyama won a sweeping election victory in August on promises of change, including reviewing the US base agreement.

US officials have said they understood Hatoyama's wish to study its details.

But Obama, who visited Japan Friday and Sunday, and his cabinet members repeatedly argued that implementation of the existing agreement benefits both nations.