Ministers from 146 countries have started five days of trade talks in the Mexican resort of Cancún by listening to an appeal from the United Nations Secretary General to open up wealthy markets to poor countries.

In a speech delivered on his behalf at the opening session of the World Trade Organisation (WTO) meeting, Mr Kofi Annan said that trade policies must give the developing world a fairer deal.

"I urge you to say 'no' to trade policies that aggravate poverty, and 'no' to practices that undermine aid. And I urge you to say 'yes' to bold but sensible steps that will revive the global economy," he said.

Despite the presence of thousands of police and soldiers around the conference centre, the opening conference was interrupted briefly by about 30 protesters against what they said was the undemocratic nature of the WTO.

This week's talks represent the half-way stage of a round of trade negotiations launched in the Qatari capital of Doha in November 2001. The WTO's director general, Mr Supachai Panitchpakdi, told the ministers that success at Cancún would give a valuable boost to the world economy.

"The outlook for the world economy remains uncertain and, despite some encouraging recent signs, we are not yet on the road to sustainable recovery," he said.

"Either we continue to strengthen the multilateral trading system and the world economy or we flounder and we add to the prevailing uncertainties. The eyes of the world are on this conference and people will judge us by the choice we make. There is only one possible answer. We have to deliver on the first choice," he said.

The hotel district of Cancún, a narrow strip of land on two sides of a lagoon, has been all but sealed off from the city centre to prevent an expected 50,000 protesters from reaching the conference centre. With temperatures in the mid 30s and high humidity, delegates are housed in a string of luxury hotels along the beach.

The EU Trade Commissioner, Mr Pascal Lamy, said that a recent deal giving poor countries access to cheap versions of lifesaving drugs sent out a vital signal about the purpose of the trade talks.

"Vital if we are to show that the WTO and the multilateral system is not just about mindless liberalisation, or kowtowing to globalisation. Of course, we have much more work to do to ensure delivery in practice, on the ground. But the deal, however long we waited for it, shows that the WTO can and will put people before markets," he said.

Mr Lamy said that the EU favoured offering special treatment to poor countries that would enable them to export to the developed world while maintaining necessary protection for home industries.

The EU is under pressure to abolish export subsidies for agricultural products and to give farmers from developing countries better access to EU markets. European farmers argue, however, that the recent reform of the Common Agricultural Policy agreed at Luxembourg represents the limit of the concessions EU negotiators should make.

The Connaught-Ulster MEP, Mr Sean O Neachtain, who is part of a European Parliament delegation at Cancún, yesterday warned the EU Agriculture Commissioner, Mr Franz Fischler, against any further move that could disadvantage farmers. "Under no circumstances can there be any unpicking of the Luxembourg agreement. Our farmers need a stable policy environment in which to plan and we can't accept any changes at the WTO that would make us go back on our promises to our farmers," he said.