Hillary Clinton condemned a wave of street violence in Northern Ireland during a state visit to Belfast.
The US Secretary of State said recent violence, sparked by a dispute over the flying of the Union flag at Belfast City Hall, showed the peace process she has long supported was not yet complete.
"There will always be differences in a democratic society, but violence is not the way to solve them. There can be no place for violence in the new Northern Ireland. The only path forward is a peaceful, democratic one," said Clinton.
However, there was renewed unrest immediately after her visit as loyalist youths clashed with riot police in Belfast city centre on Friday night.
ITV News' Political Correspondent Carl Dinnen reports:
The Democrat said violence was from "a small minority of people who try to stir up passions or emotions. It is unacceptable and must be repudiated by everyone".
"There can be no place in Northern Ireland for any violence, any of the remnants of the past need to be quickly, unequivocally condemned," Clinton told a news conference she held with pro-British First Minister Peter Robinson and his deputy, former IRA leader Martin McGuinness.
Clinton's visit to Northern Ireland, her first stop on a four-day European tour, comes amid a spate of violence.
Loyalists angry at nationalist councillors who voted to remove the Union flag atop Belfast City Hall after 100 years set fire to an Alliance party office on Wednesday.
On Thursday night, police arrested four men after the discovery of a bomb in Londonderry.
Security chiefs believe dissident republicans opposed to the peace process were planning an attack in the centre of the city.
On Friday, it was revealed that death threats had been issued to Alliance MP Naomi Long and Sinn Fein councillor Jim McVeigh.
Peter Robinson praised Clinton for her "instrumental" role in the peace process.
He said: "Very often, we will sit down, and somebody will mention someone who has claimed to be instrumental in the peace process, and Martin and I look at each other, and say 'Do you know them?'
"But you are one person who has consistently helped us. You have been a great friend to Northern Ireland."