Pets are being stolen in Northern Ireland to be used for "blooding" dogs in illegal fights involving massive sums of cash, says a charity.
This Staffordshire pittbull terrier has been bred to fight
The Ulster Society for the Prevention of Cruelty to Animals (USPCA) said the fighting dogs were openly walked in public despite being banned.
Bets of up to £10,000 are said to have been made on fights.
Pittbull Terriers bred for the illegal fights can change hands for thousands of pounds, said the USPCA.
One of the fights lasted for more than two hours, the society's Stephen Philpott said.
He said pet owners, whose animals had gone missing, may be unaware they have ended up in a "dog training camp".
Mr Philpott said one dog had nine fights within a three week period
Dozens of dogs were being stolen each year to supply the camps, said Mr Philpott.
"If a dog goes missing, it has to show up somewhere. How can all these dogs be disappearing off the face of the earth? There has to be some other reason for it... these are people's pets, lying there chained up, waiting to be fed to trained killers."
The USPCA has a catalogue of disturbing pictures showing animals which had been stolen and others which had been killed by dogs preparing for fights.
"Dog fighting has become more and more popular in certain parts of Belfast and other parts of Northern Ireland," said Mr Philpott.
"It is something that is now taking up USPCA resources and time. We have a man working on this all the time now, trying to break into the dog-fighting community."
One of the dead animals used to "blood" fighting dogs
He told BBC Northern Ireland's Nolan Show that those involved had a "dog fighter's manual".
"This was obtained as part of a planned search with PSNI. You can see the level of organisation. There are codes in it, the dogs are named and the fights are described.
"This is a very highly organised underworld. These animals exist in Northern Ireland. They fall under the Dangerous Dog Act - which is the responsibility of local government and the dog warden service.
"These animals in the photographs are resigned to a life of complete misery. They are kept purely to fight and breed."
One dog had nine fights within a three week period, according to the USPCA.
Some playgrounds in Belfast parks are now being used to train the dogs, said a city councillor.
In Ormeau Park in south Belfast, children's swings have been ripped to shreds.
In the space of one month at the end of last year, there were also similar incidents at Clara and Avoniel Parks.
Swing seats have been ripped by dogs in Ormeau Park
Alliance Party councillor Naomi Long said: "These dogs are being trained to attack children's equipment and swing seats.
"If they were to get loose in the park at a time when there were children present, the consequences could be devastating.
"I think people who get involved in dog fighting are extraordinarily cruel and brutal people."