Fans of US animated TV series Family Guy have taken to Twitter in protest at the sudden death of Brian, the Griffin family dog.

The cocktail-sipping canine with a social conscience, voiced by the show's creator Seth MacFarlane, was hit by a car and killed in an episode entitled Life of Brian, broadcast in the US at the weekend.

Ardent fans of the Fox comedy have turned to social media to express their outrage, with Twitter sites being created in honour of the recently deceased dog.

"@Brian'sDead: Brian better return or Family Guy will lose most of its viewers!" wrote one unhappy fan.

Several fans have even launched a petition urging Seth MacFarlane and Fox Broadcasting to bring Brian back from the dead.

"The writers of family guy didn't just kill off one of their creations, they killed off the dog who has lived in our homes for the last 15 years," reads the online petition. "They killed the dog we all have come to love. They killed America's dog!"

Long-time voice talents on the popular show, Mila Kunis and Seth Green were also reported to be "pretty stunned" by Brian's exit.

Producer Steve Callaghan told E! News on Sunday (November 23) that despite the fact that Brian was a much-loved central character and an integral part of the show for many years, it seemed more plausible for the Griffins' family pet to die rather than one of the Griffins themselves.

"It seemed more in the realm of reality that a dog would get hit by a car," explained Callaghan. "As much as we love Brian, and as much as everyone loves their pets, we felt it would be more traumatic to lose one of the kids."

Soon after bidding farewell to Brian, the Griffin family were seen buying a new, dog called Vinny - voiced by former Sopranos actor Tony Sirico.

Fans have also taken offence at the swift and rather insensitive arrival of the replacement dog, but Callaghan told E! News Vinny would fill the void.

"By losing Brian, it felt like a void needed to be filled, both comically and also for the interpersonal relationships between all the characters," he said. "We felt that we needed to fill that role."

Conspiracy theories have been circulating since the demise of America's favourite four-legged friend, prompted by the plotline for the December 15 episode titled Christmas Guy, which states that Stewie will hatch a plan to get "the one and only thing he wants for Christmas".

The rumour was further compounded by news that a website, supposedly created by Fox, was launching a countdown clock that promises a "special announcement from Brian" in ten days' time.

A 20th Century Fox spokesperson has however confirmed to TVLine that the website is a hoax. When asked by Deadline if Brian was likely to be brought back, a Fox representative replied: "No comment."

The shows producers had earlier said they did not fear a backlash from fans.