(05-08) 16:31 PDT LOS ANGELES (AP) --

An environmental group sued chocolate manufacturers Wednesday, contending chocolate contains potentially hazardous levels of lead and cadmium and should carry warning labels.

The suit, by the nonprofit American Environmental Safety Institute, alleges chocolate products expose consumers -- especially children -- to potentially dangerous levels of the metals.

A state investigation last year discounted the lawsuit's claims, and U.S. Food and Drug Administration researchers have found children younger than 6 who eat lots of chocolate take in 6 percent or less of the total daily amount of lead allowable by law.

An attorney for the companies named in the suit -- including Hershey Foods Corp., Nestle USA Inc., Kraft Foods North America Inc. -- said the lawsuit was baseless and an attempt to extort a settlement.

The lawsuit filed in Los Angeles Superior Court seeks in part to force the firms to include warning labels on the products under a requirement of California's Proposition 65 that individuals be warned before they are exposed to dangerous chemicals.

Scientific testing found lead and cadmium levels in products like M&Ms presented "a clear and present danger to the health of our children," said Roger Carrick, an attorney for the Palo Alto-based institute.

Michele Corash, an attorney for the chocolate companies, said the two metals are present naturally in chocolate and other food but in levels too low to pose any hazard.