Japan's central government resumed work at a disputed US military base relocation site on Okinawa on Thursday even though residents see the project as an undemocratic imposition on the small southern island.
The Defense Ministry's branch on the island said an early stage of landfill work at Henoko on Okinawa's east coast began Thursday morning.
Construction workers were setting up floats to mark the designated landfill area, making it off-limits to the public, including protesters, said Satoshi Shirakata, a spokesman at the Okinawa Defense Bureau overseeing the Henoko project.
At the centre of contention is a decades-old plan to move a Marine Corps air station from densely populated Futenma in the southern part of the island to less-crowded Henoko on the east coast.
Many Okinawans say the presence of so many US troops on the island is burdensome already and they want the air station moved off the island entirely.
Defense Ministry officials said the resumption of work at Henoko followed the central government's decision earlier this week to reverse Okinawa's earlier ban on landfill work at the site.
Okinawa Gov Denny Tamaki, who took office a month ago, has urged Prime Minister Shinzo Abe and other central government officials to stop the Henoko plan and reduce Okinawa's burdens.
In an interview with The Associated Press on Wednesday, Tamaki said the central government was not giving due consideration to other options.
"They say Henoko is the only one, Henoko is the only solution. But we think that it is definitely not the case and that they're refusing to think critically," the governor said.
"The American side has made multiple proposals under reorganization plans and the Japanese government should consider them." Washington's position is that the dispute should be resolved between Tokyo and Okinawa.
The relocation of Futenma air station was planned after the 1995 rape of a schoolgirl in which three US servicemen were convicted. The case ignited simmering Okinawan opposition to the US bases.
About half of the 50,000 US troops based in Japan under a bilateral security pact and the majority of their key facilities are on Okinawa. Residents have long complained about base-related noise, pollution and crime.
Tamaki has said he supports the Japan-US security alliance, but that Okinawa should not be the only one sacrificed.
(With inputs from agencies.)