Joe Biden made yet another of his trademark gaffes today as he met Ireland's prime minister to mark St Patrick's Day - then suggested one side of its sectarian divide was unwelcome in Washington. Sporting a green tie and noticing that everyone else was also wearing one, or clad in green, he suddenly blurted: 'Anyone wearing orange is not welcome in here.' The purported joke was a reference to Ireland's religious and political divide which was at the heart of the Troubles, the violence which killed 3,000 from the late 1960s until the start of the millennium. Orange is the color associated with the Protestant majority in Northern Ireland, and overcoming sectarian tensions has been a major part of the effort to bring peace to the once-deeply troubled province. Enda Kenny, the Irish prime minister – whose official title is Taoiseach – and his wife Fionnuala Kenny, the guests of honour, both laughed nervously. They said nothing, but continued to smile for the cameras. Scroll down for video . Wearing of the green: From left Ireland's prime minister Enda Kenny, his wife Fionnuala and vice-president Joe Biden. The vice president made a joke about sectarianism and got her name wrong . I'm with...: Vice president Joe Biden points at shamrock worn in his breast pocket to mark St Patrick's Day . After a brief pause, Mr Biden declared: 'Only joking.' He then welcomed the Kennys, Irish Ambassador Anne Anderson and the Irish entourage into the Naval Observatory in Washington, his official residence. The Vice Pesident made no further reference to his blurted-out bad joke, but at one point in his breakfast remarks appeared to refer to the Taoiseach's wife as 'Fiona', although he subsequently corrected it to Fionnuala. Northern Irish Protestants traditionally wear orange during their annual summer parades, while green is used as a symbol by mostly Catholic Irish nationalists and is a theme of St Patrick's Day celebrations around the world. In Northern Ireland, there was an immediate demand from a senior Unionist for an apology. 'Whether they were intended as a joke or not, the comments are a slur on those who would be known as 'orange' i.e. Protestants,' said the Rev William McCrea, a member of the British parliament for the Democratic Unionist Party. 'When Northern Ireland is making such an effort to make St Patrick's Day an inclusive celebration, Joe Biden's comments were disgraceful and careless,' he added. Asked about the request for an apology, an official in Biden's office said the vice president had made clear that he was joking. Biden's mother, Catherine Finnegan, was of Irish origin. Her ancestors had moved to Ireland in the wake of the potato famine. The Vice President made another minor blunder later when he read a quote from a Yeats poem he described as 'Easter Sunday 1916', when the word Sunday is not in the title. The poem was about the Easter Rising, when Irish rebels began a violent attempt to force Ireland to become independent from the United Kingdom, which succeeded five years later. It actually broke out the next day, Easter Monday, April 24 of that year. The use of Easter Sunday would materially affect the subject of the poem, best known for its phrase 'a terrible beauty is born'. He described Yeats as 'a Protestant hero in a predominantly Catholic country.' He then told the Taoiseach: 'You've become a close friend and I admire you a great deal.' Laughing: Despite the gaffe, Irish prime minister Enda Kenny laughed with Mr Biden . Mr Biden also revealed that he had a stammer as a child. 'My uncle, Ed Finnegan, a bachelor, used to sleep in the same room as my brother and I. I used to stutter very badly when I was a kid. But at night Ed used to recite the poetry of Yeats. And I would get up and recite in front of a mirror, and try to learn not to contort my face when I spoke and stuttered.' Mr Biden has a long list of previous gaffes – he once asked a wheelchair-bound local politician to stand up and acknowledge the crowd's applause, and after being chosen as Vice President he even suggested that Hillary Clinton would have been a better choice. Most recently he was widely ridiculed for putting his hands on the shoulders of Stephanie Carter, wife of defense secretary Ash Carter, and whispering in her ear as her husband was sworn in. He also told the father of a teenage girl – Utah Republican Senator Orrin Hatch's grandaughter Emily – that he hoped he had a 'big fence' as Hatch was sworn in. Five years ago, Biden incorrectly suggested at a St Patrick's Day reception that the mother of then Irish prime minister Brian Cowen was dead, saying 'God rest her soul', before correcting himself to say 'God bless her soul'. At today's Washington event the Taoiseach presented the Vice President with a book of Yeats' poetry, but told him he should not open it for at least another 25 years, 'when you are old and grey and nodding by the fire.' He then invited Mr Biden to play a round of golf in Ireland - the fifth time he has done so, with no success so far. Mr Kenny joked: 'The golf courses are still there. And they are in better condition than they have been for many years. So welcome home, Finnegan.' Mr Biden replied that last year the Taoiseach had tried to intercede for him with the president, telling him, 'You gotta let him go. You gotta let Joe go.'
Biden was supposed to be greeting Irish prime minister Enda Kenny in Washington to mark feast of Ireland's patron saint . Blurted out 'Anyone wearing orange is not welcome here' – a reference to traditional color of largely Protestant Unionists in North . Senior Protestant politician from Northern Ireland demands apology from vice-president . Also got name of Irish prime minister's wife wrong and mis-named the title of a Yeats poem he selected for the occasion .