DUBLIN— A pug-nosed black Belfast dog named Lennox, who inspired a two-year legal fight and animal-rights protests on both sides of the Atlantic, was put to sleep Wednesday amid claims that city council staff had been threatened with death.

Belfast City Council confirmed the 7-year-old dog was put down after a deadline for legal appeals expired.

Dog wardens deemed the pit bull-type dog to be a public danger and seized him from his owners in April 2010. Lennox spent two years in a municipal dog pound while his owners and city authorities battled in the courts. Northern Ireland's senior appeals judges last month upheld two 2011 rulings that the dog should be put down.

His owner, Caroline Barnes, argued that Lennox was a bull dog mix, not a pit bull terrier, never attacked anyone and could be resettled outside Northern Ireland in a jurisdiction that permits ownership of pit bulls, specifically the United States.

An online "Save Lennox" petition and social media campaigns with tens of thousands of followers, many of them using the Twitter hashtag LennoxArmy, spurred protests in Belfast and New York seeking his freedom. Among its supporters was First Minister Peter Robinson, leader of Northern Ireland's regional government, who has no role in enforcing animal welfare laws.

Barnes said the council had rejected her request to be present when the dog was put to sleep and instead would send her the ashes by mail.

City council staff said experts had found Lennox to be menacingly erratic in his behavior and a clear qualifier for the U.K.'s dangerous dogs law that bans the ownership of pit bulls or dogs similar to them. And they condemned a campaign of hate messages to council staff, which included the public naming of dog-control officers and threats to wage "war" against Belfast City Council.

"The council's expert described the dog as one of the most unpredictable and dangerous dogs he had come across," Belfast City Council said in a statement. "Over the past two years, council officials have been subjected to a sustained campaign of abuse, including threats of violence and death threats."

Councilman Pat McCarthy said Lennox's owners appeared to be in denial about the public safety risk posed by their dog.

"The people looking after Lennox for the past two years said that one minute the dog was placid and friendly, and the next he would try to get through the fence to get at you," McCarthy said. "Now, do we release that dog into society?"

McCarthy said dog catchers and other council staff had suffered campaigns of intimidation to the point where they felt obliged to flee their homes. '

'We've had petrol poured through letter boxes. We've had people named on the Web. There have been attempts to demonize our staff for doing their job," he said.

Victoria Stilwell, who hosts the Animal Planet dog-training program "It's Me Or the Dog," said she felt crushed that Belfast officials hadn't permitted Lennox's resettlement in a U.S. sanctuary for pit bulls.

"I hoped Belfast City Council would realize that there were alternatives that provided a sanctuary for Lennox in the USA where he would be safe, but they did not listen," she said.