The imminent end of the Brexit transition period risks fuelling paramilitary activity in Northern Ireland, a key watchdog panel warned on Tuesday.
The Independent Reporting Commission (IRC), established jointly by the UK and Irish governments in 2016, said Brexit has "the potential to further and greatly complicate the ending of paramilitarism" in the British province.
Northern Ireland was the epicentre of "The Troubles" -- a three-decade conflict between loyalists paramilitaries and security forces backing continued British rule and republicans intent on reunification with Ireland.
Around 3,500 lives were lost to bombs and bullets before the landmark Good Friday Agreement peace deal was sealed in 1998.
However the IRC -- set up nearly two decades later to monitor efforts against dissident groups -- warned "there are still thousands of signed-up ('sworn') members".
It also noted "paramilitarism remains a reality of Northern Ireland life in 2020".
In its annual report, the IRC said: "As the end of the Brexit transition period approaches, the possibility of a heightening of tensions reinforces the urgency of dealing with the ending of paramilitarism."
Tim O'Connor, one of its four commissioners, added: "The fact that these groups continue to exist ... constitutes heightened risk."
Brexit has the potential to drive paramilitary activity because it is a "highly emotive" issue which reawakens the "radioactive" questions of "The Troubles", he said.
Britain voted to leave the EU in a landmark 2016 referendum and ties were officially severed with the bloc in January.
However, a divorce treaty froze relations in the status quo during a transition period due to expire on December 31.
From 2021, Northern Ireland will be subject to special arrangements to prevent the re-emergence of a so-called hard border with remaining EU member Ireland -- a frequent flashpoint of Troubles-era violence.
However, some unionists have decried plans for checks on goods arriving from Britain, arguing they will create a "sea border", strain ties with mainland Britain and pave the way for a united Ireland.
Meanwhile fresh tensions have simmered between Britain and the EU after London began efforts to unilaterally change aspects of the treaty setting out the province's special arrangements.
IRC commissioner John McBurney said Brexit could be a barrier to paramilitaries disbanding, with leaders chosing to remain "on the pitch" to deal with borders resulting from the split.
The IRC report joins a chorus of claims that Brexit may upset the delicate balance of peace in Northern Ireland -- home to 1.9 million people.
Last month UK lawmakers warned that sustained terrorist activity by proscribed groups could be exacerbated by Brexit.
Parliament's cross-party Intelligence and Security Committee said any changes to the Irish border risked becoming a target and "recruiting badge" for dissident groups.
In 2019 there was renewed concern around unrest in the province when journalist Lyra McKee was shot dead during a riot in the border city of Londonderry.
Dissident republican group the New IRA took responsibility for the killing.