Pro-British loyalist militants in Northern Ireland said on Friday there had been a "spectacular collective failure" to understand their fears and anger over Brexit and other issues as police braced for more street clashes following a week of riots.
New border arrangements with EU-member Ireland must be negotiated, the Loyalist Communities Council (LCC) said in a statement.
Despite appeals for calm from London, Dublin and Washington, the nightly unrest in pro-British areas spread further into Irish nationalist parts of Belfast on Thursday, where police responded to petrol bomb and stone attacks with water cannon.
Nineteen officers and a police dog were injured, police said.
The clashes are some of the worst violence in Northern Ireland in years and have raised concern about the 1998 peace accord that largely ended three decades of sectarian and political bloodshed during which 3,600 people were killed.
The LCC, which says it speaks for the Ulster Volunteer Force, Red Hand Commando and Ulster Defence Association militant groups, said it was not involved in the riots and it called for calm.
The loyalist paramilitaries, as they are known, laid down their weapons in the years that followed the Good Friday Agreement. But the LCC said Unionist anger had been misunderstood.
"To date there has been a spectacular collective failure to understand properly the scale and nature of Unionist and Loyalist anger," it said.
The council cited concerns over post-Brexit trade barriers as well as policing following a decision last week not to prosecute Irish nationalist rivals Sinn Fein for an alleged breach of COVID-19 regulations at the funeral of a former IRA leader last June.
After the United Kingdom left the European Union at the start of this year, checks and tariffs were introduced on some goods moving from mainland Britain to Northern Ireland as the province was now borders the bloc via EU member Ireland.
British Prime Minister Boris Johnson had promised there would be no hard border between Ireland and Northern Ireland as result of Brexit, and unfettered trade between the province and the rest of the United Kingdom would continue.
But critics of the departure deal's Northern Ireland Protocol say a border is now in effect in the Irish Sea, leaving unionists, who want to stay in the United Kingdom, feeling betrayed.
"We have repeatedly urged HM Government, political leaders and Institutions to take seriously our warnings of the dangerous consequences of imposing this hard border on us and the need for earnest dialogue to resolve matters. We reiterate that message now," the LCC said.
A new protocol must be negotiated, it said.
"We again place on record our absolute determination to remove the hard border between Northern Ireland and the rest of our country that has been imposed on us by the NI Protocol."
Long Hot Summer?
With protests planned for later on Friday, one shopping mall in Newtownabbey on Belfast's northern outskirt, said it would shut early to allow staff and customers to vacate the site.
Sinn Fein leader Mary Lou McDonald said she feared the protests could set the tone for a violent summer when thousands of pro-British Protestants hold marches, a tradition the mainly Catholic nationalists who want to be part of a united Ireland see as provocative and often lead to clashes.
"We have communities that are bracing themselves perhaps for a very difficult weekend, deep concerns that violence might extend further and that this might set the tempo and the scene for this summer," McDonald told Irish national broadcaster RTE.
"There has to be a very clear call that the proposed protests for the weekend must be called off before people are badly injured or worse."
The United States, which has traditionally taken a close interest in Irish matters, on Thursday warned that the Good Friday Agreement which it helped broker should not become a casualty of Brexit.