Vehicles have been set on fire and shops looted in Dublin after a knife attack that left a number of people, including three children, injured.
A five-year-old girl and a woman in her 30s were seriously hurt in the attack after 13:40 local time.
It happened on Parnell Square East in the city centre, outside the children’s school Gaelscoil Choláiste Mhuire.
A man in his 40s who was also seriously injured is a person of interest, police said.
They added that they were not looking for any other people at this time and are following a definite line of inquiry.
Sources have indicated to the BBC that the man suspected of carrying out the attack is an Irish citizen, who has lived in the country for 20 years.
The head of An Garda Síochána (Irish police), Drew Harris, blamed the subsequent disorder on a “lunatic, hooligan faction driven by a far-right ideology”, who engaged in violence as police tried to maintain the crime scene.
The streets are now “mainly calm”, the Irish police have said, with no serious injuries reported as a result of the violence.
Ch Supt Patrick McMenamin said more than 400 officers remain on patrol after the disorder, which he blamed on “gratuitous thuggery”.
“Some of my colleagues were attacked and assaulted, thankfully none were seriously injured and I commend them all on their bravery to protect our community,” he added.
It is unclear how many arrests have been made, but Irish Justice Minister told Irish national broadcaster RTÉ that it was a significant number.
Riot police were deployed after protesters gathered in the area near the scene of the attack.
The disorder centred on several streets in the city centre, including O’Connell Street.
A number of vehicles were set on fire, including a car, a tram and a bus.
A shop on O’Connell Street was looted while the windows of other stores were smashed.
Trinity College, which is nearby in the city centre, said it was in lockdown with all gates to its campus closed due to the disturbances.
Taoiseach (Irish prime minister) Leo Varadkar said extra police resources had been deployed.
He added that he had been shocked by the knife attack and “the facts in this matter are still emerging”.
Mr Harris urged people to “act responsibly, not to listen to misinformation and rumour that is circulating on social media”.
“We know what happened, but the motive for this is entirely unclear.”
Meanwhile, the head of Ireland’s National Bus and Railworkers’ Union described those who targeted bus and trams as “thugs” and “despicable people.
Irish President Michael D Higgins said that his thoughts were with the children and families affected by the incident.
“This appalling incident is a matter for the gardaí and that it would be used or abused by groups with an agenda that attacks the principle of social inclusion is reprehensible and deserves condemnation by all those who believe in the rule of law and democracy,” he added.
The Irish National Teachers’ Organisation (INTO) said: “Our hearts are with the entire school community of Gaelscoil Choláiste Mhuire following the horrendous incident that has taken place today.”