A New Zealand-led plan to create the largest marine reserve in the world in Antarctica has stalled after two countries questioned the legal basis of the proposal.
Delegations from 25 countries have gathered for a special meeting in Bremerhaven, Germany, to consider the proposal for a 2.27 million sq km reserve in the Ross Sea.
The plan, which was developed with the US, needed approval from all member countries of the Commission for the Conservation of Antarctic Marine Living Resources to go ahead.
The negotiations take place behind closed doors. But in a rare move, commission officials spoke publicly about the obstacles to getting a consensus on the proposal.
Commission chairman Terje Lobach said Russia and Ukraine had questioned whether the members had the legal right to set up marine protected areas (MPAs) in Antarctic waters.
He believed the legal dispute could be resolved, and said that many lawyers in the negotiations confirmed the commission had the mandate to create reserves in the high seas.
Russia and Ukraine also wanted the MPA to be smaller, to have a 50-year limit, and to allow more access to fisheries.
Mr Lobach said that New Zealand and USA were considering these problems and suggested that they could make changes to the proposal.
Environment group Pew Charitable Trusts accused Russia and Ukraine of scuppering the talks.
Spokeswoman Andrea Kavanagh said: "One wonders if Russia's efforts are a stalling tactic designed to bring negotiations to a halt."
In the scientific talks which preceded the negotiations, countries debated until 5am on Sunday about the proposed reserve.
Russia's opposition prompted an open letter to Russian president Vladimir Putin signed by high profile environmentalists including director James Cameron and entrepreneur Sir Richard Branson.
The letter urged Russia - a founding commission member - to play a leadership role in helping the MPA to get over the line.
Negotiations were expected to finish tomorrow morning (New Zealand time).