The government in July plans to begin land reclamation work at the site of a controversial U.S. military base transfer in Okinawa Prefecture, sources said Saturday.

The relocation of U.S. Marine Corps Air Station Futenma from a crowded residential area in southern Okinawa faces strong opposition from local residents who want the base moved out of the prefecture entirely.

The government has already begun constructing sea walls at the Henoko coastal area of Nago, and the decision to move ahead with the land reclamation project is sure to put pressure on Okinawa Gov. Takeshi Onaga, who has promised to prevent the base transfer from happening.

Construction was delayed by Onaga's refusal to sign off on the Defense Ministry's request to relocate an endangered species of coral at the site, but Tokyo now plans to preserve the coral as is, the sources said.

That will allow construction of sea walls on a south-facing stretch of the site to finish by June, paving the way for the landfill work to begin the following month.

Plans could be delayed by adverse weather or if protests intensify. Tokyo had initially planned to reclaim a different part of the site first, but was prevented by a separate species of rare coral living there.

Okinawa hosts the bulk of the U.S. military forces stationed in Japan, a situation many local residents say puts an unfair burden on the prefecture which saw heavy casualties as a battleground in World War II.

In March last year, Onaga threatened to revoke his predecessor's approval of the landfill, and is expected to do so before work begins.