The United States plans to transfer the bulk of 4,000 out of 19,000 Marines stationed in Okinawa, southern Japan, to Guam in a period from 2024 to 2028, the commander of the U.S. Pacific Command said Wednesday.

Adm. Harry Harris told a congressional hearing that "the movement of the bulk of the Marines to Guam would occur in the 2024 to 2028 time frame."

Japan and the United States agreed in 2013 to start moving Marines from Okinawa to Guam in the first half of the 2020s as part of efforts to reduce the burden on the island prefecture, which hosts the bulk of U.S. military bases in Japan.

But the transfer is effectively tied to the planned relocation of the Marine Corps Air Station Futenma within Okinawa, a controversial project that is supposed to lead to the air base's closure and the return of its land to Japanese control, but that is fiercely opposed by locals who want the base to be moved outside the prefecture.

Speaking at the House Committee on Armed Services, Harris said the United States also plans to transfer about 3,000 Marines to Hawaii from Okinawa.

Harris expressed hope the U.S. military will reduce the number of Marines in Okinawa "ultimately" to "a point around 10,000 or 11,000."

"The whole issue of moving Marines from Okinawa elsewhere is important to our alliance relationship with Japan," he said.

"Japan has invested a lot in this," he said. "This is all about -- for everyone else's benefit -- reducing the footprint in Okinawa, and also closing Futenma."

Harris said last year the United States expects a two-year delay to 2025 in the planned relocation of the Futenma base from a crowded residential area in Ginowan to a less populated area in Nago, given strong local opposition to the plan.

Speaking at Wednesday's hearing, Harris quoted Japanese officials as saying Japan will have a replacement facility ready by Japan's 2022 fiscal year, but said, "I testified last year that I thought that that was in question."

Okinawa Gov. Takeshi Onaga has demanded that the Futenma base be moved outside the prefecture instead of being moved to a replacement facility whose construction will lead to the partial landfill of waters off Henoko.