The annual shamrock presentation ceremony at the White House was disrupted by a security alert today when an unidentified man climbed over the fence on the northeast side of the White House grounds.
He was later taken into custody.
Secret Service spokesman Eric Zahren said the man climbed over the fence on the northeast side of the White House grounds shortly after 11 a.m. before being taken into custody.
Members of the media and White House staffers, who also have offices there, were not allowed to leave the building. The regular White House briefing was delayed until the area could be secured.
Meanwhile, Taoiseach Bertie Ahern presented President Bush with a bowl of shamrock and said he hoped Congress would support a proposal that would affect illegal Irish immigrants in the United States.
Speaking the traditional handing over the shamrock ceremony in the Roosevelt Room of the White House, Mr Ahern noted the Flight of the Earls - which effectively paved the way for partition - and the settling of Jamestown, Virginia, both in 1607, were being commemorated.
He said the Flight of the Earls, which led the way to the plantation of Ulster, "effectively inaugurated the Irish diaspora"; while 100 years later Irish people began settling in Virginia.
"Each new generation of Irish arriving in this country has made is own contribution and helped assure a unique relationship," Mr Ahern said.
He said more recently arrived Irish have put down "new and deep roots".
With a presidential election next year and a new immigration bill on Capitol Hill, the issue of regularising the status of undocumented Irish - estimated to be as high as 40,000 - is rising up the political agenda.
"The resolution of this issue would mean an enormous amount to so many Irish men and women, and I fervently hope that they will, in the not too distant future, be able to step away from the shadows and into the sunshine of this great country, Mr Ahern said.
In a short speech Mr Bush, who has been guarded on the issue, avoided directly addressing the subject but recognised the historical contribution Irish people have made in areas such as education and construction.
He welcomed the friendship traditionally enjoyed between the two countries and welcomed the "strong and growing trade relationship".
Mr Ahern said the recent elections in Northern Ireland showed the people had sent an "unmistakable and undeniable" message that they wanted self-governance.
"They want their political representatives now to take responsibility together in government for building and consolidating peace."
He also recognised the efforts of American representatives such as George Mitchell in advancing the peace process and Mr Bush said he remained "ready to help".
In his address to the small gathering, which included Northern Secretary Peter Hain and Sinn Féin chief negotiator Martin McGuinness, Mr Bush said: "St Patrick's Day is an occasion that unites two distinct groups of Americans: those who are of Irish descent, and those who wish they were."
Yesterday Mr Ahern held talks with senior American politicians including Democratic Senators Hillary Clinton and Edward Kennedy and House Speaker Nancy Pelosi.
Earlier in the week he met UN Secretary General Ban Ki-Moon in New York and laid a wreath at the Twin Towers Memorial Centre.
Mr Ahern returns to Ireland tonight.