RECROP OF LON812 FILE  In this May 12, 2015 file photo, Labour Member of Parliament Jo Cox poses for a photograph. British lawmaker Cox has been injured in a shooting incident near Leeds, in West Yorkshire, England, it has been reported, Thursday June 16, 2016. (Yui Mok/PA via AP, File) UNITED KINGDOM OUT NO SALES NO ARCHIVE
RECROP OF LON812 FILE In this May 12, 2015 file photo, Labour Member of Parliament Jo Cox poses for a photograph. British lawmaker Cox has been injured in a shooting incident near Leeds, in West Yorkshire, England, it has been reported, Thursday June 16, 2016. (Yui Mok/PA via AP, File) UNITED KINGDOM OUT NO SALES NO ARCHIVE

Jo Cox, a member of the British Parliament, died Thursday after a shooting and stabbing attack in northern England. She is the first sitting parliament member to be killed since 1990, when Ian Gow was killed by a car bomb planted by the Provisional Irish Republican Army outside his home.

It remains unclear why Cox was killed. However, according to some eyewitness reports, Coxโ€™s attacker shouted โ€œBritain firstโ€ during and after the attack. That detail has sparked a wave of discussion in Britain, as the phrase โ€œBritain Firstโ€ is well-known for its links to anti-immigrant protests and is also the name of a far-right political group.

Cox, 41, was only elected to office last year but she already was considered a rising star in the center-left Labour Party.

Her previous career involved working with international charities, and she has been a vocal supporter of refugees including those from majority Muslim nations like Syria. She also frequently called upon Britain to do more to help civilians in Syria.

These positions would certainly put her at odds with many of the supporters of Britain First. The group were formed by former members of the far right British National Party in 2011 and have links to Ulster loyalist groups in Northern Ireland.

In particular, Britain First campaigns against immigration and multiculturalism. Britainโ€™s Muslim community is often a target, although the group specifically denies it is racist.

Although Britain First is far from a major political force in the country โ€” it has entered candidates in a number of different elections but has never won an elected post โ€” the group is extremely active on social media. Often, members will film themselves marching on provocative walks through large Muslim communities. Britain First likes to play on its own religious identity, describing this march and others like them as a โ€œChristian Patrol.โ€

The party, whose name is somewhat similar to the slogan โ€œAmerica First,โ€ have also said they support Donald Trumpโ€™s proposed ban on Muslim arrivals to the United States.

As hardline as Britain First may seem, it is a frequent target of mockery in the country. For example, party chairman Paul Golding recently contested the London mayoral election. When Labour Party candidate Sadiq Khan, a practicing Muslim, won the election, Golding turned his back the new mayor in a protest many found comical.

Britain Firstโ€™s levels of public support may be relatively low, but the anxiety about immigration the group presents is far more widespread.

Next week, Britain will vote on whether to leave the European Union in a referendum. Polls show an increasingly tight race that has taken many by surprise: In particular, voters who favor leaving the EU seem to be largely motivated by fears over immigration, rather than the economy.

Cox was a vocal supporter of the campaign to remain in Europe, while Britain First supported the campaign to leave it along with the more established United Kingdom Independence Party and some members of the Conservative party.