Irish Prime Minister Michel Martin warned Saturday of a "downward spiral" threatening peace in Northern Ireland, after ten days of violence amid heightened tension due to Britain's exit from the European Union.

Saturday marks the 23rd anniversary of the Good Friday Agreement of 1998, which ended three decades of "unrest" between Republicans, especially Catholics in favor of reunification with Ireland, and Protestant Unionists, which resulted in 3,500 deaths.

Martin said in a statement, "It is our duty for the generation of the convention and for future generations not to enter a vortex that takes us back to the dark era of sectarian killing and political disputes."

He added, "Those who bear political responsibilities between us must play our role and make sure that this does not happen."

The British boycott has been witnessing unprecedented violence, especially in pro-Protestant areas, where leaving the European Union raised a sense of betrayal and bitterness.

Dozens of policemen were injured.

On Friday, unionists called for an end to the demonstrations "out of respect for the Queen and the royal family" after the death of Prince Philip, husband of Queen Elizabeth II of Britain, at the age of 99.

However, clashes took place on Friday evening, but they were less intense than they were earlier in the week.

Violence has spread in recent days to Republican areas, where protesters on Thursday evening threw Molotov cocktails and stones at police forces that obstructed their advance towards unionist areas. Police used water cannons for the first time in years.

Unionists and Republicans in local governments unanimously condemned the acts of violence, and called on London, Dublin and Washington to calm down.