Campaigning in the UK on the EU referendum has been suspended following a knife and gun attack on British Labour MP Jo Cox that has left her fighting for her life.
The attack happened in Leeds in Northern England where Cox was holding a constituency meeting. Local police said a 52-year-old man has been arrested.
There are concerns that the attack may have been politically motivated with at least one eyewitness reporting that the attacker shouted "Britain First". Cox had backed the Remain campaign. The Syrian conflict was a key issue for Cox, including how to tackle the influx of refugees.
The EU referendum debate has become particularly acrimonious in recent days, in the run up to the vote on 23 June.
However, Boris Johnson, the leader of the Vote Leave campaign, told reporters his activities would be suspended, saying, "A colleague has been attacked and very seriously injured - and we've decided to suspend all campaigning. Our thoughts are with Jo Cox."
The leading Remain campaign group, Britain Stronger in Europe, announced through Twitter that they were doing the same, as did other pro and anti EU campaign groups.
According to eyewitnesses, Cox was left lying bleeding in the street after the attack, which sent a shockwave across the political world, both within the UK and the EU.
European Commission President Jean-Claude Juncker said he was, "deeply shocked by the news of terrible attack against MP Jo Cox. My Thoughts and prayers are with her husband and children."
British Prime Minister David Cameron said it was "right that all campaigning has been stopped", and cancelled a planned pro-remain rally later today in Gibraltar.
Ukip leader Nigel Farage said he was "horrified to hear of the attack on Jo Cox".
Cox is said to be in a 'critical' condition in Leeds General Hospital.
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