Frankfurt zoo flamingos beheaded

Frankfurt zoo is home to flamingos from many parts of the world

Four flamingos housed at Frankfurt zoo in Germany have been killed in an apparent attack by an intruder.

Three of the birds' heads had been torn from their bodies and a fourth bird had been strangled, zoo officials said.

"We cannot explain why someone would want to murder flamingos," spokeswoman Caroline Liefke told Reuters news agency. "It's a complete mystery."

Police are investigating the attack, which took place inside the flamingo enclosure after the zoo had closed.

Frankfurt zoo counts several flamingos in its collection, as well as larger animals such as lions, giraffes and numerous exotic birds and reptiles.