Geneva  - The United States blocked Friday the formation of a World Trade Organization panel to look into a complaint by Mexico that the US was unfairly closing its markets to tuna from its southern neighbour.

Mexico said US labeling rules, which prevent Mexican companies from placing "dolphin safe" labels on their products, violated trade rules as the tuna was in line with regulations on protecting dolphins.

About one-third of Mexico's fishing fleet was said to be adversely affected by the decision.

Mexico first asked for WTO consultation last October.

The US said its measures met its obligations under WTO rules.

The two countries have been at odds over tuna imports to the US for nearly two decades.

If Mexico makes a second request, which it can do as early as next month, the US would not be able to block the formation of a panel to hear the issue.

Meanwhile, in another dispute, the US won a partial victory against China, when a panel upheld part of its complaint regarding copyright rules.

The panel found that China was too lax regarding enforcing intellectual property rights, particularly in regards to counterfeit movies and music. However, the panel did not accept the US position that the thresholds for criminal prosecution were too high, meaning copyright violators were able to act without fear.

Also, the WTO also established a panel to look into a complaint by Thailand against the US regarding anti-dumping measures on polythylene bags. The US, as per an agreement, did not block the move. (dpa)