Nestle Purina launched an offensive this week against Blue Buffalo, accusing the rival pet food maker of lying to customers about its use of natural ingredients.

The St. Louis-based company filed a federal lawsuit against its Connecticut-based competitor, saying independent tests show that Blue Buffalo uses chicken byproducts and corn in its products — despite claims to the contrary.

Nestle Purina PetCare, a unit of Swiss-based Nestle and maker of Beneful and Friskies, is suing The Blue Buffalo Co. Ltd. for false advertising, disparagement and unjust enrichment.

According to the lawsuit, Blue Buffalo spent $50 million in national print, television and Internet advertising last year promoting its products as superior to competitors, including Purina, Royal Canin, Pedigree and Iams.