Dee Collins, Deputy Chief Constable of West Yorkshire Police, announced Cox's death in a press conference on Thursday afternoon.

The 41-year-old was shot close to her constituency advice surgery in Birstall, near Leeds in northern England, earlier in the day.

DCC Collins said the mother-of-two was reportedly shot in the face three times and attacked with a knife, adding that a full investigation was underway to establish a motive for the murder. Collins added that Cox died at 1.48 p.m. local time (12:48 UTC), within an hour of the attack.

The UK's Press Association news agency cited eyewitnesses who said the MP for the constituency of Batley and Spen appeared to be involved in a struggle in the street with a man, who pulled out a gun. Cox was left bleeding on the pavement and another man was also injured.

Police later said they believe the attack was a localized incident and they were not looking for anyone else than the 51-year-old man arrested earlier in the day, named locally as Tommy Mair. Weapons, including a firearm, were also recovered.

The Guardian newspaper reported that three named witnesses described how the attacker had shouted "Britain First," the name of a far-right, nationalist party and movement.

The attack took place in Birstall, near the northern city of Leeds

In a statement on its website later, Britain First said the media was "desperately trying to incriminate" the party in the attack, adding that it was " NOT involved and would never encourage behaviour of this sort."

Labour leader Jeremy Corbyn issued a statement saying the whole the party and country "will be in shock" at Cox's "horrific murder."

Paying tribute to her work, he said Cox "was dedicated to getting us to live up to our promises to support the developing world and strengthen human rights – and she brought those values and principles with her when she became an MP."

British Prime Minister David Cameron said his thoughts were with her husband and family.

German Economy Minister Sigmar Gabriel also tweeted his condolences to Cox's family.

French Prime Minister Manuel Valls said he was "deeply sad for Jo Cox and the British people. Through her, our democratic ideals are targeted. Never accept that!"

One of her colleagues, MP Tom Tugendhat, said he would organize a silent commemoration outside the UK House of Parliament on Thursday evening.

Cox's husband, Brendon, also issued a statement following her death.

"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. Hate doesn't have a creed, race or religion, it is poisonous," his statement read.

Cox was elected to Parliament in 2015 after a career as an aid worker for Oxfam. Part of her constituency - the town of Batley - is among the poorest in the country, part of an EU transformation zone, and has a high immigrant population.

She was critical of Britain's reluctance to deepen its involvement in the fightback against "Islamic State" militants in Syria. She also campaigned for the UK to remain in the EU.

Following the attack, both the pro- and anti-European Union camps have temporarily suspended their campaigns, with just a week to go until Britons vote on their country's membership of the bloc.

Cameron tweeted that he wouldn't attend a campaign rally on Thursday evening on the British territory of Gibraltar.

Cox is the first British politician to be killed since 1990, when the Irish Republican Army (IRA) killed MP Ian Gow in a car bombing.