US Secretary of State John Kerry has warned about risks to the Northern Ireland peace process if there are changes to the border on the back of Brexit.
Mr Kerry was speaking on Sunday during his visit to the Republic to receive the Tipperary International Peace Award for 2015.
"People need to be really careful with downstream consequences, that one choice can have an impact on other aspects and whatever happens to the border, how that border access is managed," Mr Kerry said.
"It's really critical that it be done very thoughtfully and very sensitively so that it does not have any impact."
Mr Kerry also met with Foreign Affairs minister Charlie Flanagan. The pair held bilateral discussions ahead of the ceremony.
US special envoy to Northern Ireland Senator Gary Hart also attended the talks.
On collecting the Tipperary award, Mr Kerry said: "I'm really incredibly touched, moved, very, very grateful."
Previous winners include Nobel peace prize winners Nelson Mandela and Malala Yousafzai, UN general secretary Ban Ki-moon, former president Mary McAleese and her husband Martin, and Bob Geldof.
Five groups involved in the anti-war movement in Ireland - Galway Alliance Against War, the Irish Anti-War Movement, the Peace and Neutrality Alliance, Shannonwatch and Veterans for Peace - criticised the selection of Mr Kerry for a peace award.
Mr Kerry said he was accepting the award on behalf of America, staff in the State department and White House "who labour for peace every single day".
"And for all those desperate people for whom peace can be so often be so elusive and so passionately yearned for. They are ultimately our inspiration."
