Local leaders and anti-base protesters will try to block construction work on a new air base in Nago, Okinawa Prefecture, and it could seriously damage the Japan-U.S. military alliance, Okinawa Gov. Takeshi Onaga warned on Wednesday.

“It’s not easy for the Coast Guard and riot squads to stop (anti-base protesters). I’d like to tell America that (we) will never let them build” the air base, Onaga said during a news conference at the Foreign Correspondents’ Club of Japan in Tokyo.

Tokyo plans to build a replacement base in the Henoko area of Nago for U.S. Marine Corps Air Station Futenma, which is located in the Okinawan city of Ginowan.

Onaga also said he and Nago Mayor Susumu Inamine will take every legal measure available to obstruct the construction work at the Nago site.

“It’s wrong to assume you can carry out the plan,” Onaga said, adding that is one of the key message of his diplomatic trip to Washington, which will begin on May 27.

“I fully understand (the importance) of the Japan-U.S. alliance. You should never break it down,” Onaga said.

Tokyo and Washington have agreed to relocate the Futenma base, which sits in the middle of a densely populated area, due to noise and safety concerns.

But anti-military sentiment remains strong in Okinawa, which saw fierce ground battles during World War II. A majority of locals oppose plans to relocate the base within the prefecture.

Some local leaders in Okinawa say if any local citizens are injured in a clash between anti-base protesters and Japanese or U.S. authorities defending the Henoko site, it would cause an uproar among Okinawans and could seriously damage the Japan-U.S. military alliance.

During the news conference, the governor also argued U.S. military bases, which occupy as much as 18.3 percent of the prefecture’s main island, have now become the “biggest impediment” to Okinawa’s development, rather than something essential to support the local economy.

Redevelopment of former U.S base sites, including the Naha Shintoshin area, have brought far more economic benefits to the local economy than they did when the U.S. military occupied them, Onaga said.