​It is still unclear which, if any, group is behind the unrest. But tensions have been simmering among unionists for months since the implementation of the post-Brexit trade agreement between the UK and European Union (EU).

 

The deal and the earlier Withdrawal Agreement see Northern Ireland staying within the EU's customs union for at least seven years, with customs checks on goods shipped to and from the rest of the UK.

 

That Northern Ireland Protocol is ostensibly to prevent the imposition of a "hard border" with the Republic of Ireland in breach of the 1998 Good Friday agreement that ended the decades of sectarian terrorism by Republican and Loyalist paramilitaries.

 

But this year the EU's powerful commission briefly ordered the border closed as part of its 'Vaccine War' with the UK. Days after Brussels backed down the Irish Gardai police set up checkpoints on cross-border roads and began issuing €100 fines to anyone crossing under COVID-19 rules.

 

Calls for restraint by US President Joe Biden, an outspoken opponent of Britain leaving the EU, seemingly went unheeded on Friday night.