Ministers at the trade summit in Cancun are attempting to break the deadlock on agricultural subsidies as activists mourned the suicide of a South Korean demonstrator.
Demonstrators have clashed with police
Lee Kyang-hae, the former head of South Korea's federation of farmers, stabbed himself to death during the protests, with a friend reported to have said his suicide was "an act of sacrifice" to show his disgust at the policies of the World Trade Organisation (WTO).
Groups of farmers from around the world have been among the most prominent of those staging protests outside the summit.
Government ministers are haggling over agricultural policy as serious business got underway on Thursday.
The five-day meeting began on Wednesday as several thousand demonstrators clashed with police as they tried to break through a barricade around the site of the WTO meeting.
The farming argument
Many farmers in developing nations say the large sums of money that Europe and the US give farmers suffocate their markets and keep the produce of poor countries out of international markets.
Rich countries spend $320bn on handouts to their farmers, more than six times the amount they give to poor countries as aid.
The EU and the US have promised to reform these subsidies, but their initial suggestions have been criticised for not going far enough.
Developing countries say the rich world needs to keep the promises it made two years ago to cut tariffs.
The rich world says poorer countries must agree to broader legal and commercial reforms in return for any concessions on farming.
Make or break
The 146 member governments of the WTO are trying to hammer out a new global agreement on trade - one that balances sharply contradictory demands from rich and poor nations.
Poorer countries, many of which are major agricultural exporters, realise that they have the power to derail a deal at Cancun or later, and are insisting on the WTO's commitment to reduce farm subsidies sharply.
"Sadly, the reality of the international trading system today does not match the rhetoric," said Kofi Annan, secretary-general of the United Nations.
"Instead of open markets, there are too many barriers that stunt, stifle and starve."
WTO director general Supachai Panitchpakdi said the "eyes of the world were on the conference" and that members had to "deliver".
And he said that the world's prospects for economic growth were resting on a successful meeting.
As he opened the conference, about 30 demonstrators inside the hall held up pieces of paper denouncing the WTO as "anti-development" and undemocratic.
Outside the building, there have been violent clashes between protesters and the police.
TRADE AND GLOBALISATION
Key issues at the trade talks
Protestors reportedly threw chunks of paving stones at police, who responded with tear gas.
In 1999, trade talks in Seattle were derailed by mass protests, and there has been trouble at international financial summits in Prague and Genoa.
Up to 150,000 people are expected to arrive in Cancun over the next few days.