Fears of a weekend of violent protests in Cancún have risen following violent clashes between protesters and police and the suicide of a Korean farm leader outside the World Trade Organisation (WTO) meeting.

Mr Lee Kyang-Hae, a former leader of the South Korean farmers' federation, stabbed himself to death during a demonstration against the impact of WTO rules on poor farmers.

The WTO issued a statement regretting Mr Lee's death, which came during a protest of thousands of Mexican farm workers outside the WTO meeting in the Mexican seaside resort.

Eyewitnesses said that Mr Lee, who previously went on hunger strike outside the WTO offices in Geneva, declared "The WTO kills farmers" before stabbing himself through the thorax and the heart.

The protest was mostly peaceful but when police stopped the marchers at a security barrier close to the conference venue, a small group of militant protesters associated with the Black Block attempted to storm the barrier. They pelted the police with stones and water bags and attacked the police with sticks but failed to penetrate the security cordon.

The violence came despite efforts by the Mexican farm workers' organisation Via Campesina to persuade the militants not to attack the police.

Many demonstrators were angry that their protest had been overshadowed by the violence of a small group, fearing that their message about the plight of farm workers would be lost in the subsequent reporting of the event.

Bigger protests are expected tomorrow but the authorities are confident that the geographical isolation of the conference centre, on a narrow strip of land that is easily sealed off from Cancun's city centre, should prevent any serious disruption of the WTO meeting.

A WTO meeting in Seattle in 1999 was marked by days of rioting in the city centre, prompting the organisation to hold its 2001 meeting in the remote Arab emirate of Qatar.

The WTO is a key target for the global justice movement, which argues that its rules disadvantage poor countries.