Northern Ireland officials condemned violence on Saturday after fifteen police officers were injured in clashes with loyalist protesters in Belfast.
A "small local protest" in the loyalist area of Sandy Row, south Belfast, "quickly developed into an attack on police" on Friday, police said in a statement.
The officers were "subjected to a sustained attack by rioters who have thrown a number of objects at police, including heavy masonry, metal rods, fireworks and manhole covers," said Belfast District Commander Chief Superintendent Simon Walls.
"Their injuries include burns, head and leg injuries," Walls went on.
Eight people have been arrested, police said, including children as young as 13 and 14.
“I am appealing to all those involved to stop this appalling behaviour immediately," Walls said.
“Local communities do not want to be dragged back to the past. They deserve to live in safe and peaceful areas, free from rioting, violence and wanton destruction of their communities.”
His call for calm was echoed by various government officials, including Secretary of State for Northern Ireland Brandon Lewis.
"The unrest we saw last night is completely unacceptable. Violence is never the answer," he tweeted.
Ireland's first Minister Arlene Foster also joined calls for calms, according to British media.
In parallel, unrest was reported for five consecutive nights in the unionist areas of Derry/Londonderry, with twelve police officers injured on Friday, police said.
The incidents come against a backdrop of growing discontent in Northern Ireland over the consequences of Brexit.
In order to avoid a hard border on the island of Ireland and preserve the terms of the Good Friday Agreement, the UK and Brussels agreed on a protocol that allows Northern Ireland to adhere to certain EU rules.
However, this has caused friction between the DUP and the UK government over the need for customs declarations and some checks on goods entering Northern Ireland from mainland Britain.
Tensions escalated further this week after authorities decided not to prosecute 24 members of Sinn Féin over their attendance at the funeral of former Irish Republican Army (IRA) leader Bobby Storey, despite coronavirus restrictions.
Unionists demanded the resignation of Republican Deputy Prime Minister Michelle O'Neill, who was allegedly among the 1,800 people in attendance.