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LONDON — British lawmaker Jo Cox has died after being attacked in her district on Thursday, police said.

Cox, 41, was known for social-justice campaigns and seen as a rising star in the opposition Labour Party.

Jo Cox in May 2015. HANDOUT / Reuters

Britain's prime minister called her death a "tragedy" and offered prayers to Cox's husband and two small children, as did the U.S. ambassador to the U.K.

Cox was attacked in broad daylight shortly before 1 p.m. in Birstall, not far from the city of Leeds.

"I am now very sad to have to report that she has died as a result of her injuries," West Yorkshire Police's Acting Chief Constable Dee Collins told a news conference.

A man has been arrested and police are not seeking any other suspects in relation to the attack, Collins added.

Police said weapons — including a gun — were recovered at the scene but have not provided details on a possible motive or specified the nature of Cox's injuries.

However, both NBC News' U.K. partner ITV News and the BBC said Cox had been shot and stabbed.

Cox was scheduled to hold office hours with constituents Thursday at the Birstall Library. Eyewitnesses suggested Cox may have been caught up in a scuffle between two men.

"The gun went off twice and then she fell between two cars and I came and saw her bleeding on the floor," shop owner Hichem Ben Abdallah told ITV News.

Clarke Rothwell told the BBC that the suspect, who was wearing a baseball hat, lunged at Cox with a knife after he opened fire.

“People were screaming and running from the area,” Rothwell added.

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Shortly before news of her death was announced, her husband posted a picture on Twitter of a smiling Cox posing along the river where the two shared a houseboat.

Brendan Cox later issued a statement on the beginning of a "more painful, less joyful, less full of love" new chapter for his family — but said his wife would have "no regrets" about her life.

"Jo believed in a better world and she fought for it every day of her life with an energy, and a zest for life that would exhaust most people," he said. "She would have wanted two things above all else to happen now, one that our precious children are bathed in love and two, that we all unite to fight against the hatred that killed her."

Cox entered Parliament in 2015. She is a graduate of Cambridge University and worked for international campaign organizations, including Oxfam, prior to entering politics.

She drew on her experiences in war zones in a recent interview describing why she has continued to campaign over issues such as the conflict in Syria.

“I’ve been in some horrific situations," Cox told the Yorkshire Post. "That’s the thing that all of that experience gave me — if you ignore a problem it gets worse.”

Gun violence is rare in Britain, which has strict weapons laws. The attack comes amid a heated debate over whether Britain should exit the European Union — an issue Cox has spoken out against.

Both sides of the debate suspended their campaigns after the attack to mourn Cox's loss.

News of the incident also sent shockwaves through the broader British political establishment, with lawmakers from all parties joining in to offer condolences and express their horror.

Labour leader Jeremy Corbyn lays a wreath at a vigil for slain Labour MP Jo Cox in Parliament Square in London on June 16. DANIEL LEAL-OLIVAS / AFP - Getty Images

Jeremy Corbyn, head of the Labour Party, condemned the "horrific murder" and praised Cox's "lifelong record of public service" and "deep commitment to humanity."

"Jo Cox died doing her public duty at the heart of our democracy, listening to and representing the people she was elected to serve," Corbyn said in a statement. "We have lost a much loved colleague, a real talent and a dedicated campaigner for social justice and peace."

Cameron, the prime minister and the leader of the ruling Conservative Party, sent thoughts and prayers to Cox's family over the "tragic and dreadful news."

"We’ve lost a star," he said.

London Mayor Sadiq Khan said that in the year Cox was in Parliament "she made more impact than others make in a whole" career.

"She was the best of politics," he said in a statement. "I will miss her."

American officials — still reeling from the recent massacre at an Orlando gay nightclub — added their voices to the chorus of grief and outrage.

Secretary of State John Kerry said Cox's death was "an assault on everyone who cares about and has faith in democracy."

"Our thoughts are profoundly with the family, her husband, her children and with all the British people," Kerry said Thursday at a press conference in Copenhagen.

Gabby Giffords, the former U.S. representative who survived a 2011 mass shooting, said she was "absolutely sickened" to learn of Cox's death.

"She was young courageous and hardworking," Giffords said on Twitter. "A rising star, mother and wife."

Absolutely sickened to hear of the assassination of Jo Cox. She was young, courageous, and hardworking. A rising star, mother, and wife. — Gabrielle Giffords (@GabbyGiffords) June 16, 2016

U.S. Ambassador to the U.K. Matthew Barzun said he was "heartbroken" over the loss.

We are heartbroken by the loss to her family and country of MP Jo Cox. My love and our love to them, in this time of unbearable grief. — Matthew Barzun (@MatthewBarzun) June 16, 2016

Presumptive Democratic nominee Hillary Clinton said in a statement that she was “horrified by the assassination” and that Cox was “a rising star.”

“It is cruel and terrible that her life was cut short by a violent act of political intolerance,” she said in the statement.

Oxfam, Cox's former employer, said she was “a passionate advocate for humanitarian issues including the conflicts in Darfur and the Democratic Republic of Congo.”

Cox worked for the organization between 2001 and 2009 and her husband while she worked there, according to a statement from the organization.

“She was an inspiring leader, really bringing the best out of all of us, always positive, always believing we could win, and always passionate for change,” Max Lawson, Cox’s former colleague, said in the statement.