Gardai say the behaviour of a small group of people on the streets of Dublin over the last two nights won't be tolerated.
19 people - including two under 18s - were arrested last night for public order offences in the city centre.
Glass bottles were thrown at officers and a bin was set on fire, leading to crowds being dispersed from South William Street, Temple Bar and St Stephen's Green.
Two Gardai were injured and a patrol car was damaged - while a member of the public, who wasn't involved in the violence, was assaulted and taken to hospital.
Assistant Commissioner Anne Marie Cagney says most people are being responsible - but a small minority are not: