Resentment still burns in the Ireland the Queen didn't see

Helicopters and fixed-wing aircraft patrolled the skies and snipers occupied rooftops to protect the Queen.

The fact that it is the first state visit by a British monarch since George V went to Dublin in 1911 was powerful evidence of the transformed relationship between the two countries following hundreds of years of conflict.

But despite the new atmosphere of trust and friendship symbolised by the four-day trip, there were signs of lingering resentment from extremist republican groups, who objected to the Queen's presence. A total of 21 people were arrested during several demonstrations across the Irish capital, while a pipe bomb was discovered in the luggage compartment of a bus on the outskirts of Maynooth, Co Kildare, 25 miles from Dublin.

Fears of a possible attack from dissident republicans were heightened as passengers were evacuated and a controlled explosion was carried out by the Irish army's bomb squad in the early hours of the morning.

Irish prime minister Enda Kenny condemned those who left the bomb. He added: "The vast, vast majority of people here welcome the visit of the Queen and her party. We hope that they will have a very enjoyable time here."

Snipers and armed police combed the rooftops and a church spire along Parnell Square in Dublin's inner city overlooking the Garden of Remembrance, where the Queen laid a wreath to honour those who died fighting British rule.

The atmosphere was tense as up to 300 activists gathered near the historic site.

Fireworks, glass bottles, bricks and cans were thrown by dissident supporters hemmed into narrow streets by the riot squad. Many covered their faces and held placards in support of the 32 County Sovereignty Movement - the political wing of the Real IRA, which bombed Omagh in 1998, killing 29 people and unborn twins.

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At one stage motorists, including women with children, were trapped between protesters and police, with two windows on a public bus smashed.

A police helicopter circled overhead as officers used loudspeakers urging demonstrators to disperse before the riot squad swooped in and charged at the crowd of more than 100 demonstrators. Several people, including two women, were arrested.

A known dissident republican from north Dublin was also seen by gardai driving back and forth along the city's quays in a Northern Ireland registered car.

Sinn Fein, whose national headquarters is near the garden, released black balloons into the sky as the Queen arrived.

Aengus O Snodaigh, a Sinn Fein member of the Irish parliament, said the balloons were intended to symbolise those killed by British troops in Northern Ireland and the 33 people killed in loyalist car bomb attacks on Dublin and the border town of Monaghan exactly 37 years ago.

Mr O Snodaigh said: "The fact that Dublin city is on lockdown for the week makes it clear that the relationship between the two islands is still not 'normal'.

"Sinn Fein wants to have good relations with all our neighbours, but that can only happen in an atmosphere of equality and mutual respect and with the reunification of our country."

There were minor scuffles on one of the city's main shopping streets, Henry Street, just off the main thoroughfare O'Connell Street, before republicans laid their own wreath at 16 Moore Street - the site where leaders of the 1916 Easter Rising sought refuge and eventually surrendered after the shelling of the GPO.About 150 members of socialist republican group Eirigi held a sit-down demonstration at the corner of Parnell Square, just yards from the Garden of Remembrance.

Earlier, elite army rangers - Ireland's special forces - were on patrol at Baldonnel Airport when the Queen's plane touched down around midday. They were among the 6,000 police and soldiers on duty as part of unprecedented measures to thwart any possible attacks on the monarch. About 100 officers from the Metropolitan Police have been deployed to the Republic.

A 33-motorcycle police escort led the Queen to President Mary McAleese's residence in Dublin's vast Phoenix Park through the unusually empty streets of Dublin - cleared to ensure no anti-British extremist could get close enough to launch an attack.

In addition to the explosive found on the outskirts of Maynooth, elsewhere, gardai dealt with three hoax alerts in the capital. Three courthouses in Dundalk, Monaghan and Drogheda were also evacuated before the royal couple's arrival amid concerns about suspect devices, but nothing was found after extensive searches.