A zoo in northern Germany says it appears a keeper failed to follow the "golden rule" of checking to see if lions were inside their enclosure before he entered it and was mauled.

A spokeswoman for Serengeti Park said Sunday an investigation attributed the Saturday attack to "human error," though it wasn't clear why the experienced 24-year-old keeper hadn't followed procedure.

Asta Knoth said he suffered "many deep bite wounds" from the two male lions and had undergone several hours of surgery.

Knoth told The Associated Press the man "got away lightly considering the circumstances" and is expected to make a full recovery.

The zoo is located in Hodenhagen, about 80 kilometers (50 miles) south of Hamburg.