BELFAST — Secretary of State Hillary Rodham Clinton flew here on Friday for a brief, valedictory visit that contrasted calls for peace with the discovery of two bombs unconnected with her diplomacy, underscoring the continued power of sectarian passions almost 15 years after a formal peace accord brokered partly by her husband.
The discovery of the devices elsewhere in the country came after days of chaos on Belfast’s streets when unionists, who seek continued ties with Britain, blocked traffic to protest a decision by the City Council to limit the number of days when Britain’s Union flag is flown at City Hall.
“The violence is a reminder that, although much progress has been made, the hard work of reconciliation and fostering mutual understanding must continue,’’ Clinton said after meeting some of Northern Ireland’s political leaders.
“The only path forward is a peaceful democratic one that recognizes the right of others to express their opinions but not to resort to violence,’’ she said. ‘‘There can be no place in the new Northern Ireland for any violence. Any of the remnants of the past need to be quickly and unequivocally condemned.
Hours before Clinton arrived from Dublin, four men were arrested late on Thursday when a homemade explosive device was found in the city of Londonderry, police officials said. The bomb was discovered in a car rammed by officers investigating the activities of splinter groups that have broken away from the mainstream republican movement opposing British sovereignty in Northern Ireland.
Army experts defused the bomb after nearby homes were evacuated.
The police also reported on Friday that a letter bomb had been discovered in another part of Northern Ireland after a man was observed acting suspiciously near a mailbox.
The tensions are not related to Clinton’s visit, analysts and officials said, but offer a sobering backdrop to what has been depicted as a celebratory visit recalling President Bill Clinton’s diplomatic triumphs in promoting the Northern Ireland peace in the 1990s along with the leaders of Britain and Ireland.
The causes of the current spike in tensions in Northern Ireland are diverse, but spring from familiar roots.
One issue is the opposition among dissident republicans, who seek a unified Ireland, to the designation of Londonderry as a United Kingdom City of Culture in 2013.
The name of the city is itself contentious, with Roman Catholics referring to it as Derry, its name before British authorities changed it to Londonderry centuries ago.