A plan to protect a vast swath of ocean off Antarctica by creating the world's largest marine reserve appeared headed for failure for the fourth time.

The countries that make decisions about Antarctic fishing finish a 10-day meeting Friday in Hobart, Australia.

Most favor a U.S.-New Zealand proposal to ban most fishing in a sanctuary sprawling across 517,000 square miles, or twice the size of Texas, in the Ross Sea.

But all countries must agree, which they have failed to do at three previous meetings.

U.S. delegation leader Evan Bloom said Thursday a consensus once again appeared unlikely.

"It's very disappointing from the U.S. perspective," he said.

He said a "small number of countries" opposed the proposal, but he declined to name them as the closed-door negotiations were continuing.

Russia was a key holdout in the past among the 24 nations and the European Union that comprise the Commission for the Conservation of Antarctic Marine Living Resources. Political tensions between the U.S. and Russia over Ukraine have likely only added a further hurdle this time.

Russia is one of several nations that have fishing interests in Antarctica's waters. The Ross Sea is home to the Antarctic toothfish, a lucrative species that is often marketed in North America as Chilean sea bass.

Andrea Kavanagh, director of the Southern Ocean protection project for The Pew Charitable Trusts, said it might be time to consider new approaches, such as consumers, or nations, refusing to buy fish that has been caught inside the proposed reserve boundaries.

"It's crushing that for the fourth time in three years this hasn't gotten through," she said.

The U.S.-New Zealand proposal had been a decade in the making and has gotten strong support from U.S. Secretary of State John Kerry. The proposal would ban fishing from most of the reserve while allowing for limited scientific catches in some areas.

A second proposal by Australia, France and the European Union to create four smaller reserves off the coast of the East Antarctica also appeared headed for failure.

Mark Epstein, the executive director of the Antarctic and Southern Ocean Coalition environmental advocacy group, said that while geopolitical issues were likely a factor this time, it was too soon to give up on the consensus approach.

"Our profound hope is that all the members will come back to the original reasons and meaning for creating the convention," he said.

The convention was established in 1982 with the express objective of conserving Antarctic marine life.

The Russian delegation could not be immediately contacted for comment Thursday.