OSAKA — A key U.S. senator involved in Japan relations said Wednesday evening the appointment of Foreign Minister Takeaki Matsumoto comes at a critical moment for both countries.

Jim Webb, chairman of the Senate Foreign Relations Subcommittee on East Asian and Pacific Affairs, voiced regret over the resignation of Foreign Minister Seiji Maehara, long considered in Washington as one of the Democratic Party of Japan's strongest supporters of the U.S.-Japan alliance.

Matsumoto's appointment came as congressional frustration is growing over the lack of progress on completing the 2006 agreement to realign U.S. forces in Japan. The agreement calls for 8,000 marines in Okinawa to be transferred to Guam but is contingent on Japan providing a replacement facility at Henoko for the Futenma base.

At a Senate Armed Services Committee hearing in Washington on Tuesday, Webb and Sen. Carl Levin, the committee chairman, voiced concern over the lack of progress on the relocation to Guam.

"This issue is one of the most serious problems in our relationship with the Japanese and also in Japanese domestic priorities. You can see the turbulence it has put at the very top of the Japanese government because we have not yet resolved (the Futenma) issue," Webb said.

Levin expressed concern not only over the political situation in Tokyo but also local opposition to the 2006 accord.

"Opposition is so strong in Okinawa that it seems to me the prospects aren't great that the Futenma replacement facility will happen this fiscal year," he said.

U.S. officials who deal with Okinawa have privately said no movement on Futenma is likely until after this spring's assembly election.