Coldplay's Chris Martin and Jonny Buckland on a Cancun beach

The WTO meeting in Cancun will discuss how to break down global trade barriers.

"Free trade is a great idea. It's just that we in the West do anything but stick to it," said Martin.

The Coldplay members spelt out the word "hope" in giant green letters on a beach near the summit venue on Tuesday.

They have also gathered more than three million signatures for a make Trade Fair campaign during their recent world tours.

It's very hard to find things that rhyme with 'North American Free Trade Agreement' Coldplay's Chris Martin

"We'd like to raise awareness about the idea of more fair trade around the world," Martin said.

The band delivered the petition to WTO director general Supachai Panitchpakdi.

The WTO summit will see representatives from more than 146 countries try to work out agreements to liberalise trade across the world.

Good songs 'priority'

Critics say current trade rules are hurting poor countries by making it hard for them to sell products in Western markets fairly.

Martin, the partner of Hollywood star Gwyneth Paltrow, said the band were committed to supporting fair trade, but were unlikely to do so in song.

"It's very hard to find things that rhyme with 'North American Free Trade Agreement'," he said.

"Our priority is to write good songs. Because if we didn't we wouldn't get invited to meetings like this," Martin said.

Coldplay, who have toured the world promoting their second album, A Rush of Blood to the Head, which was released last year.

The album was nominated for the UK and Ireland's Mercury Music Prize on Tuesday night, which was won by garage star Dizzee Rascal's Boy in Da Corner.