The beleaguered Irish economy is facing a major policing bill as the entire operation for the Queen's visit this week and next week's overnight visit by US President Barack Obama is expected to be close to €30m.

Already, large parts of Dublin have been sealed off and the PSNI in Northern Ireland and the Gardaí in the Irish Republic are also maintaining close surveillance on known terrorists as part of the security countdown to the visit of the Queen tomorrow.

A senior Gardaí officer said: "We are now entering the crucial phase of what is the biggest security operation we have ever mounted, with 8,000 members involved.

"Contingency plans are in place to ensure that the schedule is not disrupted by potential attackers or troublemakers."

However, President Mary McAleese - who finishes here second and final term of office this year - hailed the Queen's trip (pictured here in Belfast, by Brian McCalden) as an "extraordinary moment" in the history between the two countries, as unprecedented steps were taken to ensure the historic visit runs smoothly.

The Taoiseach, Edna Kenny, said that the State visit represented the start of a new era between both countries based on respect, friendship and mutual recognition of two countries having normalised relations.

"It also symbolises the healing of the past, a recognition of two counties having grown up together and two countries who face the future together," he said.

The Taoiseach also commented on Ireland's economic challenges - but didn't refer directly to the cost of security for the two visits.

On the country's EU/IMF bailout deal, he told Sky News: "We are able to be on track and to meet the requirements of the bailout agreement, obviously the question of interest rate reductions are being pursued by the Minister for Finance."

The reality is however, that the cost of the two operations is huge - with around 4,000 police officers on duty overall and some 500 troops last night ringing the perimeter of Baldonnel military aerodrome near Dublin for the arrival of the royal flight.

Soldiers from an Istar surveillance company went into action on light tactical armoured vehicles, fitted with sophisticated equipment.

A Giraffe air defence system is also on standby, with another located at Farmleigh in the Phoenix Park, where the Queen is due to spend the three nights of her stay here.

Gardai also brought forward plans to clear the streets around the Garden of Remembrance at Parnell Square in Dublin city centre as a result of indications that protesters intended to turn the first stop on her itinerary into a flashpoint.

Officers began erecting barriers around the square and North Frederick Street from Saturday morning and by yesterday the area had been restricted to all road traffic, with access limited to pedestrians after a small group of 70 demonstrators, mainly drawn from the socialist republican group eirigi, staged a protest in the city centre yesterday afternoon, but were well-policed and dispersed without trouble.

More than 30 streets around the city were cordoned off over the weekend with parking restrictions remaining in place for the visit in areas including the north and south quays, Nassau Street, Pearse Street, Dame Street, Thomas Street, James's Street, Gardiner Street, Mountjoy Square and Conyngham Road.

More than 5,000 manholes, culverts and drains have been checked and sealed in the four counties and lampposts have also been examined as potential hiding places for guns or explosives, while cyclists have also been warned not to leave their bikes chained to posts or railings.

In Co Tipperary, Irish police are also increasing security around the Rock of Cashel ahead of the visit.

She will also travel to a horse stud farm as part of her three-day visit.

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(BMcC/GK)