Okinawa Gov. Takeshi Onaga on Friday criticized Prime Minister Shinzo Abe and U.S. Defense Secretary Jim Mattis for agreeing to proceed with the long-delayed plan to relocate a contentious U.S. base within Okinawa Prefecture.

Onaga told reporters in Washington that it was "regrettable" Abe and Mattis agreed earlier Friday in Tokyo to advance the bilateral plan, which moves U.S. Marine Corps Air Station Futenma from a crowded part of Ginowan further north to Henoko, a coastal area of Nago.

"If they stick to the view that Henoko is the only solution to resolve (the base issue), it will leave serious problems in the future," Onaga said.

Onaga spoke after meeting with State and Defense department officials in charge of Japanese affairs in Washington.

These officials "reiterated the United States' unwavering commitment" to building a replacement facility for the base in Henoko and told him that moving Futenma to Henoko "is the only solution that addresses operational, political, financial and strategic concerns and avoids the continued use of Marine Corps Air Station Futenma," according to the State Department.

Onaga, who has demanded the base be moved outside Okinawa, relayed local opposition to the relocation plan to Joe Young, director for Japanese affairs at the State Department, and Paul Vosti, acting director for Japan in the office of the Under Secretary of Defense for Policy.

The governor said he held talks with a total of 13 members of Congress during his five-day visit to Washington through Saturday.

Aside from the Futenma issue, Abe and Mattis agreed that the two countries will work together to reduce the U.S. military's footprint in Okinawa, which hosts the bulk of U.S. military facilities in Japan.