Around 21,000 people protested against the planned relocation of a U.S. military airfield within Okinawa Prefecture on Sunday ahead of U.S. President Barack Obama's visit to Japan, in a sign of growing local frustration over the new Japanese government's vague stance in reviewing the transfer plan.

The protesters called for the immediate closure of the U.S. Marine Corps' Futemma Air Station located in a downtown residential area of Ginowan and urged Prime Minister Yukio Hatoyama to reject the transfer of the facility to a coastal zone in Nago, northern Okinawa, in his talks with Obama slated for Friday in Tokyo.

Demonstrators braved the heat to pack into an open-air theater in a seaside park in Ginowan, central Okinawa, and adopted a resolution stating, "The small island of Okinawa doesn't need a base any more. We oppose the construction of a new facility in the Henoko (district of Nago) and (Futemma's) relocation within Okinawa."

They accused U.S. Defense Secretary Robert Gates of "intimidating" the Japanese government over the relocation issue when he pressed Japan last month to stick to a 2006 bilateral deal on the Futemma transfer and to resolve the matter before Obama's arrival.

Under the 2006 pact, the two countries agreed to transfer the heliport functions of the Futemma facility to the Marines' Camp Schwab in the less densely populated city of Nago by 2014.

The rally brought together the heads of U.S. base-hosting local municipalities as well as Diet members elected from Okinawa who belong to the ruling Democratic Party of Japan and its coalition partners -- the Social Democratic Party and the People's New Party.

The DPJ, which came to power in September after a sweeping election victory, has promoted the idea of moving the Futemma airfield out of Okinawa or even out of Japan, even though it would go against the 2006 accord signed as part of the realignment of U.S. forces in Japan.

But Hatoyama has recently appeared evasive on the issue, saying Tokyo will take time to consider the matter, as the issue has developed into a major headache for bilateral relations.

Foreign Minister Katsuya Okada said in a television program earlier in the day that Hatoyama and Obama are likely to skip in-depth discussions on the Futemma relocation during their talks because they are unlikely to find a breakthrough.

Okada has complicated the issue by advocating merging the Futemma functions with the nearby U.S. Kadena Air Base. The proposal had been considered but dismissed during past negotiations between Tokyo and Washington due to operational difficulties and local protests.

Over 2,000 people staged a rally Saturday in the town of Kadena in protest against Okada's proposal.

While Okinawa makes up only 0.6 percent of Japan's land mass, it accounts for around 75 percent of the land area for facilities exclusively used by U.S. forces in Japan.