The university that granted Mexican President Enrique Pena Nieto a law degree in 1991 says he copied texts and ideas without crediting their authors in his thesis.

The PanAmerican University said Sunday that Pena Nieto's failure to properly credit parts of texts included in his thesis did not violate university rules in force at the time.

The university's statement did not use the word "plagiarism," but did say his thesis included "textual reproductions of fragments (of other works) without footnotes or mentions in the bibliography."

The university suggested that rules had become tighter, but noted "our university's general rules do not apply to ex-students" and said "this is an old case which cannot be subject to any action."