The cost of the massive security operation to protect the Queen and President Barack Obama when they visit the Republic later this month is estimated to reach almost €30m (£26.2m).

Finance chiefs in Dublin have agreed to allocate extra funding after intense discussions with senior officials from the Republic’s Departments of Justice, Foreign Affairs and Defence.

However, the final total will not be known until the visits are over and costs such as overtime are collated.

“At this stage it is not possible to say specifically how much expenditure will be involved and the full costs will not be known until after the visits have taken place,” said Justice Minister Alan Shatter.

“While the financial requirements will undoubtedly be significant, the safety of the Queen and the President will be the paramount considerations involved for the gardai and the State, he added.”

Senior security sources estimated last night that close to 7,500 people will be involved in the security plan, including gardai, military personnel and civilian employees.

Justice and Foreign Affairs officials have been liaising with senior gardai over the past seven weeks as they prepared the groundwork for the two visits.

Contingency planning for the likely arrival of the two VIPs has been under discussion for more than 12 months, it has also emerged.