A British member of parliament Jo Cox, a vocal advocate of Britain's membership in the European Union, was shot dead in the street of West Yorkshire on Thursday, forcing suspension of campaigning for next week's referendum on the country's EU membership.
Jo Cox, 41, a lawmaker for the opposition Labour Party, was attacked by a man called Thomas Mair, who is alleged to be a "dedicated supporter" of a neo-Nazi group based in the United States.
Media reports said the MP was stabbed before she was shot dead.
Cox was attacked while preparing to meet constituents in Birstall near Leeds in northern England, reports said.
West Yorkshire regional police said Mair, the 52-year-old attacker, was arrested by officers nearby and weapons, including a firearm recovered. "We are not in a position to discuss any motive at this time," said temporary chief constable Dee Collins.
Reports quoting an eye witness said the man pulled an old or makeshift gun from a bag and fired twice. "I saw a lady on the floor like on the beach with her arms straight and her knees up and blood all over the face," Hichem Ben-Abdallah told reporters. "She wasn't making any noise, but clearly she was in agony."
The lawmaker's husband Brendan 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."
Both supporters and opponents of Britain's EU exit said were suspending activities for the day, with the `Remain' camp saying its activities would also be suspended on Friday.
Prime Minister David Cameron said he would pull out of a planned rally in Gibraltar, the British territory on the southern coast of Spain.
Cameron said the killing of the mother-of-two, who had worked on US President Barack Obama's 2008 election campaign, was a tragedy.
"We have lost a great star," the Conservative prime minister said. "She was a great campaigning MP with huge compassion, with a big heart. It is dreadful, dreadful news."
Thomas Mair, the alleged killer of Cox was a "dedicated supporter" of a neo-Nazi group based in the United States, the Southern Poverty Law Centre, a civil rights group, said.
The group said Mair had a "long history with white nationalism".
"According to records obtained by the Southern Poverty Law Centre, Mair was a dedicated supporter of the National Alliance (NA), the once premier neo-Nazi organisation in the United States, for decades," the legal advocacy group said on its website.
It was not immediately clear what the impact would be on the 23 June referendum, which has polarised the nation into pro- and anti-EU camps. But some analysts speculated it could boost the pro-EU "Remain" campaign, which in recent days has fallen behind the "Leave" camp in opinion polls.
Britain's sterling currency rose against the dollar after news of the attack, adding around two cents.