Cat owners are being urged to be extra vigilant after yet another spate of mystery pet killings in the region.

More than 20 animals are believed to have been deliberately killed in the Bristol area alone this year.

In the latest series of incidents, nine cats were found dead with suspected anti-freeze poisoning, or have had to be put down, in the Brislington area of the city.

The deaths have led to a warning by vets at Bristol-based Highcroft Veterinary Group.

They follow similar worrying incidents in North Somerset where 29 pets were targeted in Weston-super- Mare, Clevedon and Bridgwater in August 2008.

Nine cats died on the Bournville estate in Weston after consuming anti-freeze and 19 were killed in nearby Bridgwater over the summer months, all found with anti-freeze in their stomachs.

RSPCA investigators say those cats could have been deliberately poisoned.

At the time, owners in Bridgwater were warned to keep pets indoors.

The vets have no idea how the Bristol cats came to be poisoned by anti-freeze but there are a number of possibilities.

A spokesman said: "One is that they had been drinking water from a pond that had anti-freeze added to it to avoid it freezing over in the cold weather.

"The practice is urging all cat owners to be vigilant when handling anti-freeze products and to look out for spillages or leaks.

"It is very palatable to cats as it tastes sweet but it is extremely poisonous."

Anti-freeze poisoning causes acute kidney failure and by the time the clinical signs are apparent it is almost always too late to treat successfully – treatment would need to be within minutes of ingestion.

Any cat owners worried that their cat is behaving strangely – vomiting, not eating, lethargic, wobbly or having seizures – should contact their veterinary surgeon, or call Highcroft on 01275 832410.

Other incidents include a kitten in Withywood, Bristol, which had to have a leg amputated after it was shot, shortly before two other cats in the area disappeared.

In February, the Western Daily Press reported how 13 cats were found dead or dying in Little Stoke, again from possible poisoning.

Christine Bayka, who runs The Moggery cat rescue centre in Bishopston, Bristol, called the police and the RSPCA after learning of the deaths.

Four animals were found locked in a shed in The Avenue, apparently having been starved, and there have been reports of half a dozen others found dead nearby.

The Moggery is offering a reward for information leading to a prosecution.

Ms Bayka, 57, was called after the starved cats were found and since learned a cat had been found dead in Queensway and five cats had been found dead in Brookcote Drive, one with a stake through it.

In the spate of attacks last August, five animals, all from homes in Bath Road in Bridgwater, died in the space of seven days after ingesting the liquid from a mystery source in the area – sparking fears that the family pets were being targeted by someone.