TOKYO, Jan. 21 — Tokyo is pushing ahead with plans to relocate a controversial U.S. base on the southern Japanese island of Okinawa, despite the weekend re-election of a mayor strongly opposed to the move, and on Tuesday invited tenders for the first stage of work.

Delays in relocating the U.S. Marines' Futenma air base, a move first agreed between Tokyo and Washington in 1996, have long been an irritant in U.S.-Japan ties.

Japanese Prime Minister Shinzo Abe is keen to make progress on the project as he seeks tighter ties with the United States in the face of an assertive China.

Chief cabinet secretary Yoshihide Suga told a news conference on Tuesday that bids for the first phase of construction, a landfill project, were now open.

"We are thinking that we want to proceed with the relocation as smoothly as possible," he added.

Susumu Inamine, a staunch opponent of the relocation, was re-elected mayor of the Okinawa city of Nago, defeating an opponent who backed the project and ran with the strong support of Abe's Liberal Democratic Party (LDP). His win is a potential headache for Abe and may cause friction with Washington.

"The plan must go back to square one," Inamine told reporters on Sunday. "I will reject all procedures that are premised on the landfill project."

Last month, Okinawa Governor Hirokazu Nakaima approved a plan to move Futenma's functions from a populous part of central Okinawa to Nago's coastal Henoko area.

Preparations for any relocation, such as surveying, could take a year, with the first relocation work starting after that. Japanese media says the government hopes to begin this in 2015, but Inamine's election could cause delays.

Seeking to soothe discontent, Abe's government earmarked 348 billion yen ($3.34 billion) for Okinawa's economic development in the draft budget for the year from April and pledged about 300 billion yen per year through 2021/22.

Abe also promised to study whether the relocation plan could be sped up and said the government would start talks with the United States on a deal that could allow for more oversight of environmental issues at U.S. bases.