Gardaí are expecting protests ahead of the Queen's historic visit to Croke Park this afternoon.
There has already been some clashes between Gardaí and Eirigi protestors near the War Memorial Garden in Islandbridge.
Violent clashes on Dublin's O'Connell Street and Dorset Street yesterday afternoon resulted in the arrest of 21 people.
Twenty of those appeared before a special court sitting last night, charged with public order offences.
Gardaí are expecting more protests today ahead of the Queen's visit to Croke Park, the site of a British massacre of Irish civilians in 1920.
The public order unit is on standby and Gardaí say they will not tolerate any violent protests or disturbances.
Earlier, Queen Elizabeth laid a wreath in honour of 49,400 Irish soldiers who died fighting in World War One.
UN veterans were among the dignitaries invited to today's ceremony at the War Memorial Gardens in Dublin.
Today's service at Islandbridge was requested by Buckingham Palace as part of Queen Elizabeth's State visit.
A military band played 'God Save the Queen' and 'Amhrán na Bhfíann' while the British monarch and President Mary McAleese laid commemorative poppy wreathes – one red, one green in honour of the dead.