Making one of her last foreign trips as U.S. Secretary of State, Hillary Clinton arrives in Northern Ireland to show support for the province's fragile peace.
But violence broke out just hours before her arrival when pro-British loyalists, enraged at a decision by nationalist councillors to remove the Union Jack flag from above the entrance of Belfast City Council, battled with police.
A number of police officers were injured and four people were arrested.
An office belonging to the non-sectarian Alliance Party, whose support enabled the nationalists' vote to bring down the British flag, was also ransacked and set on fire during the rioting.
Northern Ireland remains riven by sectarian tensions and Clinton arrives in a week that has seen three riots.
Straining tensions further, police seized a home-made bomb in a car on Thursday night.
Clinton is set to meet politicians from both sides of the political divide during her trip.
Hillary Clinton visits Northern Ireland amidst unrest (1:05)
Dec. 7 - U.S. Secretary of State Hillary Clinton arrives in Belfast to lend support to the province's fragile peace, amid rioting and unrest. Sarah Sheffer reports. ( Transcript )