A British member of Parliament was shot and stabbed, then airlifted to a hospital while holding an event, the BBC reports.

Jo Cox, Labor MP for Batley and Spen, was attacked outside a library on Thursday in Bristall, West Yorkshire, the Independent reports.

UPDATE: ABC News reports that Cox has died of her injuries.

The attack occurs as British leaders are grappling with a proposal to leave the European Union. Cox is a vocal opponent to what has been called “Brexit,” or Britain exiting the union.

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The Mirror reports Cox’s attacker shouted “Britain first,” citing witnesses.

The Yorkshire Post reports Cox is in critical condition and a 52-year-old man has been arrested in connection with the attack.

The Independent reports the attacker appeared to be using an adapted replica or a homemade gun.

Brexit has emerged as a topic as Britain deals with migrants from abroad, but Cox has posited that leaving will not solve any problems.

“I am pro staying in the EU,” Cox told the Huddersfield Daily Examiner in February. “For me the Prime Minister has got it all wrong — Britain is a big and strong country and we usually come out on top when it comes to decisions being made. I’ll be passionately supporting the campaign to stay in the EU.”

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Earlier this month, Cox penned an editorial for the Yorkshire Post supporting Britain staying in the EU.

“But I strongly believe that concerns about immigration – as legitimate as they are – are not a reason to vote for Brexit. This is why,” she wrote. “First, because leaving the EU won’t solve the problem. Over half of all migrants to Britain come from outside the EU, and the result of this referendum will do nothing to bring these numbers down… Please don’t fall for the spin prior to June 23 that the only way to deal with concerns about immigration is by voting to leave – that simply is not the case.”

June 23 is the day United Kingdom leaders will vote whether to stay or leave the EU.