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.