Participants in an Easter Monday march in the Northern Irish city of Derry lobbed Molotov cocktails at an armoured police vehicle, a police spokesman said.
The authorities had not been notified beforehand of the march, organised by republican groups.
The Northern Ireland police had warned in recent days of the possibility of violence against officers on Easter Monday.
Northern Ireland commemorated on 10 April the signing of the Good Friday Agreement between London and Dublin, which ended years of deadly violence in the region exactly 25 years ago. The symbolic anniversary also falls on Easter Monday, a traditional day of protest for Irish Republicans, in reference to the 1916 Easter Rising.
Rivalry between Catholic nationalist paramilitaries (grouped under the Irish Republican Army, IRA) and Protestant loyalists led to much bloodshed in Northern Ireland from the 1960s. Altogether, more than 3,500 people were killed and 40,000 wounded. The Good Friday Agreement mandated the disarmament of paramilitary groups on both sides, police reform and a power-sharing within the Irish government of unionists and nationalists.
Although political tensions between the two sides have remained high in recent years, heavy violence has been rare. On Tuesday night, US President Joe Biden is expected in Belfast to hail the peace agreement and the progress made since then.
