The gardaí had no intelligence suggesting there would be trouble at yesterday's Love Ulster march in Dublin, Assistant Garda Commissioner Al McHugh said today.
He said gardai had met the organisers of the march, Fair (Families Acting for Innocent Relatives), and were told there would be no sectarian or paramilitary banners displayed.
He said the Grada knew Republican Sinn Féin were staging protest against the parade
"The intelligence that was available to us from different sources including the PSNI that no high grade marching or protesting was going to take place on the day," Mr McHugh told RTE radio.
Green Party Spokesperson Ciarán Cuffe said the gardai should have been aware of the potential for violence and where the flash points would be.
"Republican Sinn Féin had voiced concerns about violence in advance of the March, and information was available to suggest that violence would occur.
"There was a wealth of information available on the web in the days prior to the march, and on the streets yesterday morning which suggested that violence might occur," Mr Cuffe said.
He said Garda Commissioner Noel Conroy should launch an inquiry into the policing operation.
Mr McHugh also associated himself with the view that the parade was hi-jacked by trouble makers with no particular political agenda.
Many media reports say Garda clashed with republicans abetted by youths and thugs but Mr McHugh said most of the rioters were "non-party" and he noted that many of those arrested were under 18.
He denied that O'Connell St should not have been used because of the improvements works which provided blocks, paving stones and other forms of ammunition for missiles for rioters.
He said numerous agencies were consulted in the lead up to the march including Dublin City Council. The council had, he said, made reasonable efforts to secure the sites of work.
He was supported by Minister for Justice Michael McDowell said he was "absolutely satisfied" the Garda had no prior knowledge of the events that unfolded.
He also pointed out that the Taoiseach Bertie Ahern's claim that rumours were abound in his constituency about riots, were only known to him after the event.
He said O'Connell St would remain a place were people could march. "We can't have a group of thugs on the margins of Irish politics deciding who does have civil liberties in our society and who doesn't," Mr McDowell said.
The Minister for Foreign Affairs Dermot Ahern said the riots were an attempt bring the sectarian tension of the North sounth of the border.
"It was a crass and deeply misguided attempt to radicalise, to drive people to the extremes. The scenes on Saturday must bolster our determination to stamp out sectarianism throughout the island," Mr Ahern said.