TOKYO (AFP) - The top US diplomat for Asia was due to meet Japan's foreign minister on Thursday for talks amid a worsening row over an American military airbase on the southern island of Okinawa.

Kurt Campbell, the US Assistant Secretary of State for East Asia and Pacific Affairs, was in Tokyo ahead of next week's visit by President Barack Obama.

Campbell was to meet Foreign Minister Katsuya Okada, who this week cancelled a visit to Washington for talks with Secretary of State Hillary Clinton, with Tokyo citing scheduling conflicts because of a parliamentary session.

Washington and Tokyo have been close security allies in the post-war era, and the United States has about 47,000 troops based in Japan, more than half of them on Okinawa, where their presence has often rankled local residents.

Japan's new government, which took power in mid-September, has promised to review a 2006 pact on rejigging the US troop presence, with the flashpoint being the Marine Corps Futenma Air Base located in an urban area of Okinawa.

Under the previous bilateral agreement, the base is due to be shifted to a less-populated coastal area of Okinawa by 2014 -- but Japan's new government has said the base may have to be moved off the island or even out of Japan.

Senior US government and military officials have repeatedly said Washington is in no mood to renegotiate the base relocation agreement for Okinawa, considered a strategic location close to China, Taiwan and North Korea.