Top trade officials from the European Union, the United States and other nations are set to meet in Zurich on Monday in a further effort to resolve differences ahead of the WTO's December conference in Hong Kong, which they are still hoping will cap four rocky years of negotiations.

The aim is to "talk candidly," said a senior US government official. The 148 nations in the WTO set the rules for world trade.

The informal Zurich gathering comes on the heels of one in Paris last month, where officials made slim progress largely because of persistent disagreement over the farm trade.

Much of the deadlock there was tied to divisions between the United States and the EU over tariffs and government aid for farmers, with each side pushing the other to make concessions.

Crawford Falconer, chairman of the WTO's formal farm talks, has said it is an open question whether they can produce a result by December.

They may have got down to real bargaining but should have reached such a point six months ago, he told a WTO meeting last week.

The WTO's Doha Round talks, launched in 2001 in Qatari capital Doha, aim to produce a treaty cutting customs duties, subsidies and other barriers to commerce. The plan is also to use trade to lift developing countries out of poverty.