Irish riot police have driven back hundreds of anti-capitalist demonstrators protesting at Saturday's historic enlargement of the EU.
It is reportedly the first time Irish police have used water cannon
They directed a water cannon into the crowd near the Phoenix Park venue for the EU summit before a phalanx of officers with shields forced it back.
Irish police said 28 people were arrested over public order offences.
A female police officer was injured during the riot, which broke out at the end of a largely peaceful day.
The BBC's Kevin Connolly reports that for most of the day, the police watched good-naturedly as the protesters, at most about 2,000 in number, paraded in the bright sunshine near the perimeter of the park.
The protesters waved black and red flags and banners saying "No borders, no nations, against a Europe of capital".
Some of the marchers, most of them of student age, wore masks and scarves over their faces.
However, the mood suddenly changed in mid-evening at a gate into the park where several hundred protesters faced off with police.
It was a surreal standoff in a leafy avenue of detached houses, our correspondent notes, and at one point a water cannon, borrowed from Northern Ireland's police, was used to contain the crowd.
Anarchists and anti-capitalists were among the protesters
Inside the compound, the EU leaders were dining and it is unlikely they heard anything of the disturbances, our correspondent adds.
Almost half of the Irish Republic's entire police force was on duty in Dublin for the summit.
Cian O'Callaghan, a male protester who wore a curly pink wig, miniskirt and pink tights for the demonstration, suggested the heavy police presence had provoked people.
"The government put so much effort into trying to scare people away from peacefully protesting, it was all the more important we came out today," he was quoted as saying by AP news agency.