Political leaders must get out of Stormont and engage with their disillusioned grassroots, US Secretary of State Hillary Clinton has said.
She added: "What we have to do is get out of the ballrooms, out of Stormont and into the communities where people live, where they do not have that lasting hope of optimism."
It comes amid fresh violence on the streets of Belfast, with attacks on the cross-community Alliance Party and the discovery of two bombs in Londonderry and Co Down.
Mrs Clinton said she wanted to continue to work with political leaders to help progress the peace even after she stands down from politics next year.
She said: "There is a lot to be proud of but I want to offer a cautionary word because if we do not focus on a community level, on that interface, we will not have really achieved the peace that has been worked for. I want to remain involved as a friend, advocate and cheerleader for what we already achieved. Let us reach out to those who do not yet feel in their heart what has been achieved."
Earlier, the US Secretary met Alliance Party MP Naomi Long, who is under threat from loyalists over her party's stance on a controversial vote to restrict the flying of the Union flag over Belfast City Hall.
Among the 500 guests at the lunch which was organised by the Worldwide Ireland Funds were former first minister Ian Paisley, 1972 Olympic gold medallist Dame Mary Peters and Nobel Peace Prize winners John Hume and David Trimble.
Mrs Clinton, who said she was impressed by the steady, common-sense leadership provided by Northern Ireland's First and Deputy First Ministers at Stormont, was presented with a Worldwide Ireland Funds lifetime achievement award in recognition of her commitment to peace and reconciliation.