Barack Obama has been forced to leave Ireland early due to fears Airforce One could be grounded by a new volcanic ash cloud blowing down from Iceland.
The US president flew to London on Monday evening just hours after he received a rapturous reception in central Dublin from more than 25,000 people during a speech in which he pledged that America would continue to stand by peace-makers in Northern Ireland.
A White House spokesman confirmed that concerns over the ash cloud from the Grimsvötn volcano forced the presidential entourage to make a swifter than expected exit from the Republic.
He had been expected to stop off Tuesday morning at Glasnevin cemetery en route to the airport to pay homage at the crypt of Daniel O'Connell, in an acknowledgement of the 19th century Irish nationalist leader's role in opposing the slave trade.
It was not the first time in the daythat the president's travel arrangements had to be changed somewhat hastily.
Earlier, the presidential Cadillac, nicknamed "the Beast" for its bomb-proof features, failed to make it out of the US embassy in Dublin after getting stuck on a ramp.
The Obamas had to abandon the car in front of waving crowds and switch to another vehicle to drive them to the Marine One helicopter that took them to visit his ancestral home in Moneygall, County Offaly.
Back in Dublin at the end of a packed day, Obama told thousands gathered in Dublin's College Green that "America will stand by you always in your pursuit of peace". Earlier the president had described the peace process in Northern Ireland as a "ripple of hope" to people trapped in other conflicts across the world.
In a show of solidarity with some of the key players in the peace process before his speech, Obama met briefly with Northern Ireland's first minister, Peter Robinson, and the deputy first minister, Martin McGuinness.
Addressing the crowds gathered near Ireland's first parliament and close to Trinity College, Obama said: "Ireland, you need to understand that you have already passed the world's highest hopes. A dream has turned to a reality because of the work of this nation."
To the delight of thousands who continually chanted "Obama, Obama" even before he took to the podium at teatime, the president said: "This little country that inspired the biggest things – your best days are still ahead of you."
Obama also praised the work of the late taoiseach Dr Garret Fitzgerald, who died last week, for pioneering the peace process in Northern Ireland.
At the start of a week when he seeks European help to resurrect the Middle East peace process, the president emphasised "how inspired we have been by the progress that has been made in Northern Ireland. Because it speaks to the possibilities of peace and people in long-standing struggles being able to re-imagine their relationships."
Referring to the pint of Guinness he drank earlier in a pub in Moneygall, Obama told his outdoor audience in Dublin: "I feel even more at home after that pint that I had. I feel even warmer."
While the crowds were kept off the route that the Queen and the Duke of Edinburgh travelled on through Dublin last week, Obama drew large numbers of adoring admirers.
Thousands had queued patiently in the streets of central Dublin for a chance to see the president in the flesh from early Mondaymorning. They had to pass through security cordons controlled by sharply dressed US secret service officers in sunglasses who were standing at airport-style checkin centres. In one part of Dublin the crowds snaked past the city's Olympia Theatre all the way back to Christchurch Cathedral and then back on to Dame Street.
Among those waiting to pass through the security checks was Dubliner Aaron Heffernan who not only bore an uncanny resemblance to Obama but even dressed like the president in a long, black Crombie coat, black gloves with an American flag pinned to his lapel. Even his hair cut was the same.
"I came here to get some inspiration as I want to stand for the presidency of Ireland this October," the 21-year-old drama student said. Putting on his best Obama voice, Heffernan added: "Don't say a 21-year-old can't be president of Ireland. As the man would say himself – Yes we can!"
The majority of those filing up towards the tented security area were children, young people and families, including a group of secondary school pupils from St.MacDarat's school in south-west Dublin who admitted they had bunked off their lessons to see the president.
On Dame Street, Yasmine Leonard, 16, said she had been waiting since 9am to get a chance to see Obama. "I think he is amazing and it's educational for me to be here as I am learning something. It's like a history lesson so I haven't missed my studies," she added.
Her friend Phillipa Allen from the Greenhills district said she would rather see the president than Irish singing superstars Jedward, who were on the bill to entertain the waiting crowds before Obama took to the stage. "The president is far, far cooler than the Jeds," she said.
