FIFA president Sepp Blatter says five Mexico footballers who tested positive for clenbuterol did so because they ate food that was ''definitely'' contaminated, and he says he backs the decision of the Mexico Football Federation to exonerate the players.

Blatter is in Mexico for Sunday's final of the under-17 World Cup.

''It's definitely a case of food contamination,'' Blatter said. ''It is a warning, especially an economic one for different countries that export meat.''

The Mexican federation said Friday it would not punish the five players, who tested positive during a training camp in May.

Tour de France champion Alberto Contador also blamed contaminated meat for his positive test for clenbuterol last July.

Blatter said FIFA agreed with the decision and said the world governing body had a copy of Mexico's report on the incident.

The five players - goalkeeper Guillermo Ochoa, defenders Edgar Duenas and Francisco Rodriguez, and midfielders Antonio Naelson and Christian Bermudez - were banned from playing in the Gold Cup in June in the United States. Mexico went on to win the regional championship, defeating the United States 4-2 in the final.

Clenbuterol has been used to accelerate growth in animals.

Mexico President Felipe Calderon has acknowledged that contamination is a problem in the country.