The US yesterday told Japan the planned relocation of a US marine airbase and thousands of troops based on the southern Japanese island of Okinawa was not up for negotiation in a further sign of growing tensions over the future of the US military footprint in east Asia.
Reports said the US secretary of state, Hillary Clinton, told the Japanese ambassador to Washington, Ichiro Fujisaki, that Japan must honour a 2006 agreement to move the Futenma airbase - located in a crowded city on Okinawa - to the island's remote east coast.
Fujisaki told reporters the discussion had centred on "the importance of US-Japan" ties, but Clinton reportedly made it clear that the US expected "swift implementation" of the existing accord.
Last week, the Japanese prime minister, Yukio Hatoyama, said he needed more time to determine the base's future following electoral promises to lessen the Japanese dependence on US foreign policy.
The original $10.3bn (£6.4bn) relocation plan would also see the transfer of 8,000 marines and their families to the US Pacific territory of Guam by 2014.
Discussions about the relocation began well over a decade ago amid mounting opposition to the US military presence on Okinawa, which hosts more than half the 47,000 US troops in Japan.
The bases are routinely blamed for noise and air pollution, and residents live with the threat of a catastrophic accident.
Although serious crimes are relatively uncommon, attitudes changed after three US servicemen were convicted of raping a 12-year-old Okinawan girl in 1995.
The Japanese defence minister, Toshimi Kitazawa, said Tokyo had set itself a May 2010 deadline to decide the base's future, but added that he hoped an agreement would be reached sooner.
Japan's decision to postpone a decision has been met with an exasperated reaction by US military officials.
Last week, General James Conway, the commandant of the US marine corps, said the delay was "unfortunate", adding, "The Futenma replacement facility is absolutely vital to the defence that we provide for the entire region."
Hatoyama's indecision is also harming his popularity at home, about six months before upper house elections that could give his Democratic party of Japan control of both houses of parliament.
In a poll published by the Mainichi newspaper yesterday, 68% of respondents said they were concerned about ties with the US.
The Futenma debacle and Hatoyama's handling of the economy saw his cabinet's approval rating slide to 55%, down 9% from last month, the poll revealed.
Almost four months after his party swept to power in a landslide election victory, Hatoyama appears no closer to reaching a decision on Futenma.
He could choose to honour the original agreement, but the delay suggests he is more sympathetic to moving the base to another part of Japan.
The social democratic party, a junior partner in Hatoyama's coalition government, supports moving the base out of Japan and has threatened to leave the coalition if the existing accord is implemented.
Barack Obama's irritation was evident earlier this month when the US president snubbed an offer from Hatoyama to explain his thinking on Futenma's future on the sidelines of the climate change summit in Copenhagen.