Story highlights The dog was taken from the family home two years ago

Pit bull-type dogs, among others, are illegal in Northern Ireland

Lennox never bit anyone, lawyers for the family argued

A campaign to save the dog went viral, with protests in New York

An international effort to save a dog on death row in Northern Ireland ended in failure, heartbreak and recrimination Wednesday when Lennox -- described by the Belfast City Council as a "dangerous, illegal pit-bull terrier type" -- was put to death.

The dog's owner, Caroline Barnes, told CNN she was devastated by the decision to kill an animal she described as a well-behaved family pet. Lennox was taken from the Barnes family home in Belfast by dog wardens two years ago after city council officials identified him as a pit bull-type dog, which is illegal in Northern Ireland.

The case provoked outrage from dog-lovers across the globe. Barnes' "Save Lennox" campaign went viral, attracting the support of celebrities, lawmakers and almost 200,000 people in an online petition. Vigils and protests were held by animal rights activists on both sides of the Atlantic, including demonstrations outside the British and Irish consulates in New York, to plead for Lennox's life.

"Animal rights groups have even staged protests in New York about this. We did everything possible to save Lennox but they still wouldn't listen," said Barnes.

However, the struggle -- which involved several court hearings -- ended when the council confirmed the 7-year-old dog had been "humanely put to sleep."

JUST WATCHED Lennox the dog put to sleep Replay More Videos ... MUST WATCH Lennox the dog put to sleep 01:01

"This was in accordance with the Order of the County Court which was affirmed by the Northern Ireland Court of Appeal," said a statement issued by the council Wednesday.

The statement added that the council's expert "described the dog as one of the most unpredictable and dangerous dogs he had come across... The council regrets that the court action was necessary but would emphasize that the safety of the public remains its key priority."

Northern Ireland's First Minister Peter Robinson turned to social media in a doomed, last-minute attempt at intervention.

"As a dog lover I am very unhappy with the outcome of this case," he tweeted. "Spoke to Lord Mayor about Lennox. Suggested BCC (Belfast City Council) should seriously look at re-homing option. Why exercise the order if there's an alternative?"

The council was so determined to kill Lennox, Barnes said, that "they wouldn't even listen to the man responsible for running the country."

Celebrity trainer Victoria Stilwell of Animal Planet's program "It's Me or the Dog" traveled to Belfast to make her own personal appeal for clemency, describing Lennox as "an historically unaggressive American bulldog-labrador mix."

"Victoria was willing to take Lennox under her care in the United States at no expense to the council but they even turned that down as well," Barnes said.

Lawyers for Barnes argued that the dog had never bitten anyone and had behaved well since being impounded, but in June, Northern Ireland's top court rejected a bid from Barnes to overturn the decision of two lower courts condemning Lennox to death.

A 28-day deadline for legal appeals expired at midnight Tuesday. The dog was put to sleep at a secret location, the council said.

Barnes said all legal options had been exhausted and the "heartbroken" family finally had to admit defeat.

"We are devastated and disgusted by the way we have been treated by Belfast City Council. They wouldn't even let us say goodbye to Lennox."

In its statement Wednesday, the council claimed that some staff members had been threatened because of the Lennox case.

"Over the past two years, council officials have been subjected to a sustained campaign of abuse including threats of violence and death threats," said the statement.

The council added it was "in ongoing contact" with Northern Ireland police regarding the alleged incidents.