OXFORD, England (Reuters) - Agriculture is likely to provide some of the most difficult issues to resolve in trade talks between the United States and European Union, Irish farm minister Simon Coveney said on Tuesday.

The two sides held a third round of talks in Washington last month as they work towards the world's biggest free-trade deal that could boost their struggling economies by dramatically increasing transatlantic business.

"We want to see a trade agreement between the European Union and the U.S. but certainly agriculture is difficult," Coveney told reporters at the annual Oxford Farming Conference.

"In particular beef in terms of what we find acceptable and hormone use," he added.

Ireland and the United States are both major beef exporters.

The EU has ruled out importing meat from animals injected with hormones and said that it will not simply open the door to genetically modified crops. So far, the EU has allowed just two crops to be grown in Europe. A potential third has been awaiting approval for 12 years.

EU farm commissioner Dacian Ciolos told reporters it was too early to talk about the results of the negotiations but stressed the importance of not relaxing EU standards.

"We have a very high level of standards. We are very attentive to maintain those standards in all negotiations including with the U.S.," he said.

(Reporting by Nigel Hunt; editing by Keiron Henderson)