HONG KONG (Reuters) - The United States and the European Union sparred on Wednesday over farm subsidies, food aid and measures to help the world's poorest countries, souring world trade talks that were already in trouble.

EU Trade Commissioner Peter Mandelson warned that the World Trade Organization (WTO) may even fail to achieve the one goal that seemed within reach for the group's six-day meeting in Hong Kong -- a package of measures to help least developed countries.

South Korean protesters tried for a second day to reach the venue of the convention center, but they were beaten back by riot police with pepper spray and batons.

Many of the protesters fear for their livelihoods as their countries' traditional industries, like rice production in South Korea, are exposed to global competition.

But others, like HIV-positive Cambodian sex worker Chuon Neth who wants access to life-prolonging anti-retroviral (ARV) drugs, were in Hong Kong to demand even freer trade. "Because of WTO rules Cambodia cannot buy cheaper ARVs from countries like India but only from rich countries like the USA," she said.

Police spokesman Alfred Ma said there were no injuries and no arrests on Wednesday, but added: "The signs are telling us that it (the violence) is likely to escalate."

Still, there has been no repeat of the violence that marred a 2003 meeting in Cancun, Mexico, where talks on a deal to reform world trade and lift millions out of poverty almost collapsed.

The Hong Kong meeting, which opened on Tuesday, was initially intended to approve a draft free trade treaty freeing up business in farm and industrial goods and services.

That plan was abandoned because of differences between rich and developing countries -- particularly over the EU's resistance to further cuts in import tariffs on farm goods -- though the 149 nations of the WTO still hope to reach a deal by the end of 2006.

"I believe either we move forward or we risk moving backward toward protectionism that will stunt economic growth and harm the developing world most," he said in his speech to ministers.

But there was little prospect of a breakthrough in the row over market access for farm goods, on which the 25-nation EU says it will not budge until developing nations offer more access to their markets for industrial goods and services.

Brazil, which has spearheaded a developing countries' drive to win more access for their farm goods, slammed the "remnants of feudalism" and "unacceptable privilege" of rich nations.

"Rich countries cannot expect to receive payment for what they should have done anyway long ago," Foreign Minister Celso Amorim said. "Poor countries cannot wait for another 20 years to see true reform in agricultural trade. The time to act is now."

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