The WTO on Thursday set up a panel in a renewed attempt to settle a dispute over US "dolphin friendly" labels which allegedly hit imports of Mexican-caught tuna, trade sources said.

The United States rejects Mexican charges that it has failed to fall into line with a 2012 ruling on the issue by the World Trade Organization's dispute settlement body.

As a result, Mexico asked the Geneva-based WTO to set up what is known as a compliance panel to assess Washington's respect for the May 2012 decision.

Tuna sold in the United States must carry a dolphin-safe stamp, which Mexico argued successfully in 2012 was an illegal means to keep out imports.

US legislation on the importation, marketing and sale of tuna and tuna products was adapted in the wake of the WTO decision.

Washington insists that its amendments brought its law into line, and that consumers have the right to know that their tuna was caught in a manner that did not harm dolphins.

Given its directly opposed reading of the US changes, Mexico asked for a review by the WTO, which polices respect for global trade rules in an effort to offer its 159 member economies a level playing field.

Washington won an initial bout, but that victory was overturned on appeal in 2012, with the WTO's dispute settlement panel of independent trade experts finding that the labelling rules afforded less favourable treatment to Mexican-caught tuna.

The main problem, the WTO said, was that the US measures were not even-handed in the way in which they address the risks to dolphins arising from different fishing techniques in different areas of the ocean.

The stakes are high because the tuna trade with the United is worth billions of dollars, according to Mexican officials.

Disputes at the WTO are often highly complex and technical, and can last for several years amid appeals and assessments of compliance with its rulings.

In the event that the WTO's disputes settlement body finds in favour of a plaintiff, it has the power to authorise retaliatory trade measures against a country if it fails to fall into line.

The tuna battle is one of the world's oldest trade disputes, having been launched in 1991 at the GATT, out of which the WTO was crafted in 1995.