CANCUN, Mexico -- Trade ministers from across the globe sought last-minute alliances Tuesday ahead of a World Trade Organization meeting, while opponents mapped out plans to derail the event in this Caribbean resort.

Some 4,700 delegates from the WTO's 146 member nations are holding a five-day meeting, starting Wednesday, with the aim of breaking the deadlock in the current round of trade liberalization negotiations.

Ministers held private meetings in small groups Tuesday to fix their positions ahead of the hard bargaining that is expected over the next few days.

The biggest issue is likely to be agriculture, where almost every country has its own interest and many are contradictory.

Meanwhile, police increased security throughout Cancun, setting up various roadblocks to keep activists opposed to the WTO away from the delegates.

Anti-globalization campaigners, farmers and labor rights promoters plan a week of protests, saying trade can also increase poverty, encourage mistreatment of workers and the environment, and diminish cultural diversity.

Banging drums and chanting slogans against the WTO, some 1,000 anarchists and leftists marched Tuesday through downtown Cancun but were forced back before reaching the site where WTO delegates will soon be meeting. Protesters say the WTO benefits big business at the expense of poor nations and the environment.

WTO meetings have regularly attracted protests since Seattle in 1999, when the meeting was badly disrupted by thousands of protesters rioting in the streets.

The British rock group Coldplay, participating in a campaign called Make Trade Fair, turned over to the WTO on Tuesday a petition of more than 3 million signatures urging members to create rules that benefit developing nations.