Three men are expected to face animal cruelty charges after they were caught red handed slitting the throat of a sheep in an illegal abattoir on Tuesday.

After discovering the bloody scene, animal welfare officers also spotted two men who turned up to buy meat that was hanging in a non-refrigerated room in an abandoned farm in the Swieqi valley.

Officers also noticed the testicles of a horse on the ground. In a field neighbouring the room was a mound of butchered animal heads and limbs that were covered in manure, animal welfare officer Godric Marston said as he stood outside the farm that was cordoned off by police.

An old donkey, three horses, four goats and a sheep grazed in a nearby field although it is not clear whether they were about to be slaughtered.

Animal welfare department director Mario Spiteri said the officers had been keeping an eye on the farm for several months following complaints that illegal dog fighting could be going on there.

On Tuesday they inspected the abandoned farm, situated just off the road cutting through the Swieqi valley, and found lots of blood on the ground of a tiled room.

"It was not just drops of blood but pails full of it. We immediately suspected it was an illegal slaughter house. There were also tools used to kill animals and animal tags used at the abattoir to ensure the traceability of the meat," Mr Spiteri said. It was not clear whether the tags belonged to the state abattoir or whether they were fake.

Animal welfare and police officers turned up at the farm again yesterday, at 7 a.m., and caught the three men killing the sheep. They were not wearing gloves and did not seem to have taken sanitary precautions, Mr Marston said.

One of the men insisted he had a licence to slaughter animals, Mr Spiteri said adding that, in any case, it was illegal to kill animals outside the state abattoir.

Mr Spiteri explained that the department intervened since the way the animals were being killed - by slitting their throats - was in breach of animal welfare regulations. In the state abattoir, animals are first stunned before they are killed.

The three men are expected to be charged with animal cruelty and breaching health regulations by selling meat that was not slaughtered in monitored sanitary conditions.