A swan had to be put down after it was savaged by a dog and left to die in a country park.

Police and RSPCA officers are trying to track down the owner of the dog, which attacked the bird on Saturday afternoon at Watermead Country Park, in Birstall.

Calie Rydings, of the RSPCA, said: "This animal was badly mauled and effectively left to die. We need to trace the owner of the dog which is responsible for this sickening attack. It is important we do all we can to try to ensure this dog does not do this again."

Police said the dog ran on to a frozen lake and attacked the swan, leaving it injured and covered in blood, at about 3pm on Saturday.

A member of the public contacted a park ranger, who rang the RSPCA and the police. The fire service was also called as the bird had become frozen to the ice 20ft from the shore and needed to be rescued.

It is not known if the bird became frozen to the ice, on a lake in the northern section of the park, at the Wanlip Road end, in Syston, before or after the dog attack.

Fire crews from Syston and Leicester attended. A fire service spokesman said firefighters used an inflatable path to get themselves and an RSPCA officer out to the swan. The officer released the injured animal from the ice using a hook, and brought the swan to the shore.

Ms Rydings said the swan was taken to a local vet, who decided the bird was so badly injured it needed to be put down.

She said: "It is a criminal offence under the Animal Welfare Act to cause unnecessary suffering to an animal.

"The offence carries a punishment of a fine of up to £20,000 or up to six months in prison.

"It is clearly a very serious matter and a very serious attack. There was a lot of blood, so the owner of the dog may have been aware the swan was badly hurt.

"We urgently need to talk to this person and to make sure they understand about keeping a dog under control in a public place."

A Leicestershire police spokesman said: "Officers are appealing for the owner of the dog, believed to be a white and tan bull mastiff or similar breed, to contact them to discuss the incident."

A spokesman for Leicestershire County Council, which looks after the northern section of the country park, said: "We are saddened by this incident and understand an investigation into what happened is taking place.

"We want everyone to enjoy Watermead and advise dog owners to keep their pets under control.

"If you see swans being fed, or see them on the embankment, we would advise you to put your pets on to on a lead until you have walked by."

Anyone with any information on the dog attack can contact Pc Jason Edwards on 101.