Tributes were paid yesterday to Daniel Patrick Moynihan, the former United States senator from New York, who died on Wednesday, aged 76.
Senator Moynihan, who took a keen interest in Irish affairs, was a leading Democrat in the Senate for 24 years and a former US ambassador to the United Nations.
The Taoiseach, Mr Ahern, said his death was a sad loss. "He was a great intellectual and a great friend to Ireland".
Mr Moynihan was part of an informal group of senior Irish-American politicians known as the "Four Horsemen" who played an active part since the late 1970s in promoting Irish interests in Washington.
The Fine Gael leader, Mr Kenny, said he was saddened to learn of Mr Moynihan's death. "He will be remembered as a great friend of Ireland and a courageous opponent of republican terrorism," he said.
Mr Kenny added: "His tireless commitment to finding a peaceful solution to the conflict in Northern Ireland was instrumental in encouraging the US government to become involved in supporting the peace process."
President Bush said Mr Moynihan had been an "intellectual pioneer". "He committed his life to service and will be sorely missed," he said.
A prominent liberal, he was the only politician to serve at the highest levels of four successive US administrations, under Presidents Kennedy, Johnson, Nixon and Ford.
Since his retirement in 2001, Mr Moynihan had been a senior scholar at the Woodrow Wilson International Centre for Scholars. He was also a professor at Syracuse University.
Mr Moynihan grew up in Hells Kitchen in New York. A veteran of the US Navy, he will be buried next Monday at Arlington National Cemetery.
"We have lost a great American, an extraordinary senator, an intellectual and a man of passion and understanding about what really makes this country great," Senator Hillary Clinton, who succeeded Mr Moynihan in the Senate, said.