England is being plagued by an alleged serial killer targeting cats and small animals.

So far, 400 animal deaths have been attributed to the attacker.

The unknown killer has been given a number of names in the media, including the Croydon Cat Killer, Croydon Cat Ripper, and M25 Animal Killer and the UK Cat Killer.

How long as this been happening?

Reportedly, about two years.

Animal charity South Norwood Animal Rescue and Liberty (SNARL) report the killings started in 2015 in south London's Croydon.

At first, six cats that were missing and were then found dismembered were thought to have been attacked by foxes, the BBC reported.

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SNARL said since then, cats, rabbits and foxes had all been killed in the same way in other parts of England including, Surrey, Hampshire, Kent and Sussex.

And because the animals were all found mutilated in a similar way, they believed it was the work of one person.

What is happening to the animals?

The alleged killer reportedly strikes mainly at night, using pet food to attract the animals.

Cats were found decapitated, with their paws and tails cut off, or sliced open.

The animals' bodies were often found at or near their owners' homes.

What are the police doing?

The UK's Metropolitan Police have launched Operation Takahe specifically aimed at nabbing the animal killer.

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SNARL are also helping with the investigation.

A new forensic lab in Surrey has also been established to examine the animal corpses, the Guardian reported.

In November, Northampton Police warned pet owners to keep their cats, guinea pigs, rabbits and other small animals, including dogs, inside at night.

Are people at risk?

Detective Sergeant Andy Collin, who is leading the investigation, said he feared if a person was responsible, they might become tired of animal victims.

"If you look at offending patterns, the assumption is this killer is getting some form of gratification," he told UK media.

"The concern is they will cease getting that gratification and escalate the attacks to humans, specifically vulnerable women and girls."

There are no reports the attacker has harmed humans so far.