US President Barack Obama has used an open-air speech in the Irish capital to reaffirm US-Irish ties, at the start of a week-long tour of Europe.Mr Obama praised the Irish people for striving to overcome sectarian differences and financial difficulties.
He was addressing thousands of cheering people in Dublin's College Green.
Mr Obama then flew to London Stansted airport, earlier than expected to avoid any delay from an ash cloud being emitted from a volcano in Iceland.
After three days of high-level talks and meetings with Prime Minister David Cameron and the Queen, he will visit Poland and then France, where he will attend a meeting of the Group of Eight (G8) major world powers.
Earlier on Monday, the US leader visited Moneygall, a small village in County Offaly that was home to one of his ancestors who emigrated to the US in 1850.
Tight security To cheers from an exuberant thousands-strong crowd in Dublin, the US president began his upbeat evening address with the greeting: "Hello Dublin! Hello Ireland! My name is Barack Obama of the Moneygall Obamas, and I've come home to find the apostrophe that we lost somewhere along the way."
He then said in somewhat stilted Gaelic that he was happy to be in the Republic of Ireland.
"Whenever peace is challenged... America will stand by you always in your pursuit of peace," he said.
The Obamas had landed in Dublin earlier on Monday amid tight security following the US raid that killed Osama Bin Laden in Pakistan three weeks ago.
Mr Obama met Irish President Mary McAleese, and also held talks with Taoiseach Enda Kenny.'Special relationship' On Monday afternoon, crowds lined the streets in Moneygall - which has just 300 residents - to welcome the Obamas to the village that was home to the president's great-great-great grandfather, a shoemaker.
Locals greeted Mr Obama and First Lady Michelle Obama with cries of "Welcome home!" as they entered the village.
The couple visited the ancestral home of the Kearney family, shook hands with well-wishers lining Moneygall's flag-bedecked main street and enjoyed supping on a pint of Guinness - or a half, in the first lady's case - in Ollie Hayes' pub, one of the village's two drinking establishments.
There was a minor delay to the schedule when a bomb-proof Cadillac that was part of the presidential cavalcade became stuck on a ramp on the way out of the US embassy in Dublin. The US Secret Service later denied this was the president's vehicle - known as The Beast - and that the mishap had forced the US first couple to switch vehicles.
Moneygall, County Offaly
- Village of 300 residents, 140km (90 miles) south-west of Dublin
- Moneygall has two pubs, but no bank, cash machine or petrol station
- President Obama's great-great-great-grandfather on his mother's side was a shoemaker in Moneygall
- His son, Falmouth Kearney, emigrated to New York in 1850 at the age of 19 at the height of Ireland's Great Famine
- President Obama was given a guided tour of the old Kearney family home and met extended family members
On their three-day state visit to the UK, the Obamas will spend time at Buckingham Palace as guests of the Queen.The US president will hold talks with Prime Minister David Cameron at 10 Downing Street.
In a joint article to be published in The Times on Wednesday, the two men hail the UK-US partnership as "not just a special relationship, it is an essential relationship - for us and for the world".
The bilateral co-operation, they write, is founded on a "deep emotional connection, by sentiment and ties of people and culture. But the reason it thrives, the reason why this is such a natural partnership, is because it advances our common interests and shared values".
Mark Mardell, the BBC's North America editor, says Afghanistan will be high on the agenda in Mr Obama's discussion with Mr Cameron, as will Nato's operation in Libya and the upheaval in the Arab world.
The US leader will also address both houses of the UK parliament at Westminster Hall.
It is rare for a foreign head of state to make such an address in Westminster Hall - usually this is reserved for British monarchs.
Relations reset On Thursday Mr Obama heads to Deauville, France, for the G8 summit where he will meet French President Nicolas Sarkozy, Russian President Dmitry Medvedev and Japanese Prime Minister Naoto Kan.
On Friday, the US leader travels on to Poland to discuss proposals for a US missile shield in Europe which the Poles will partly host.
President Obama hopes to press the reset button on relations with some US allies, after appearing to take the UK and the rest of Europe for granted, says our North America editor.
Security for the tour is expected to be unprecedented, following the US raid that killed al-Qaeda leader Osama Bin Laden in Pakistan earlier this month.
In an exclusive interview with the BBC aired on Sunday, Mr Obama said he would order a similar operation if another militant leader was found in Pakistan.
The killing of Bin Laden in a Pakistani garrison town strained ties between the two allies.