Trade powers have launched an eleventh hour effort to rescue global trade talks in Germany, with the US saying it is hopeful of progress.
US Trade Representative Susan Schwab joined counterparts from the European Union, Brazil and India to begin five days of closed-door talks on the Doha round of free trade negotiations.
Representatives of Japan and Australia are due to join them on Saturday.
The fate of the Doha round could depend on whether the so-called G4 group can resolve differences this week on agriculture that have haunted the talks since they were launched more than five years ago in the capital of Qatar.
WTO boss Pascal Lamy has warned that without a breakthrough very soon, the round could be put on hold for several years.
Negotiators are also set to discuss two other pillars of the talks - services and non-agricultural market access (NAMA), or manufactured goods.
They have received less attention due to the insistence of developing countries that a deal to slash rich country farm subsidies and tariffs comes first.
The ministers are meeting in Potsdam, near Berlin, at the Schloss Cecilienhof palace, where allied leaders plotted Europe's future after WWII.
Washington has demanded that any deal that significantly cuts US farm subsidies must open new export markets around the world in agriculture, manufacturing and services.
Campaign group Action Aid said a majority of negotiators from poor countries believe the WTO round, called the Doha Development Agenda, had failed in its aim of fighting poverty.
