The Catholic Primate, Dr Sean Brady, condemned recent killings in Northern Ireland as "evil and brutal" at an ecumenical service in Armagh last night attended by the President, Mrs McAleese.
Dr Brady, the Archbishop of Armagh, said it was "a particularly difficult time in the history of our land" but said that those who wanted peace, justice and reconciliation were stronger than those who wanted violence, injustice and hatred.
"We ask the Spirit to remind us that those who want peace and reconciliation outnumber those who oppose them.
"We must not forget that fact and we must stand in solid support of the peace-makers," Dr Brady said.
Asking people to pray for the victims and their loved ones, he added: "We beg God that these evil and brutal killings may come to an end."
RUC marksmen were positioned around the grounds of St Patrick's Cathedral in Armagh as Mrs McAleese arrived for the ecumenical service to mark the week of prayer for Christian unity.
She was given a civic welcome to the city at the door of the Archbishop's Palace by the Lord Lieutenant for Co Armagh, Lord Caledon; the head of the Northern Ireland Civil Service, Mr John Semple; the deputy leader of the SDLP and local MP, Mr Seamus Mallon; the Mayor of Armagh, Mr Pat Brannigan, and the chief executive of Armagh District Council, Mr Dessie Mitchell.
After attending a dinner hosted by Dr Brady, Mrs McAleese took part in the ecumenical service, where she gave the first reading.
Clergymen of each Christian denomination were led by the Rev Herbert Cassidy, the Church of Ireland Dean of Armagh; the Rev Anthony Davidson, of the Presbyterian Church and the president of the Methodist Church in Ireland, Dr Norman Taggart.
The president of the Irish Council of Churches, the Rev David Nesbitt, also attended.
Pupils of Catholic and Protestant schools in Armagh took part in the service and the homily was given by the Catholic Bishop of Helsinki, Dr Paul Verschuren, who spoke on church unity.
Mrs McAleese was accompanied by her husband, Martin.