The interest rate demanded by investors in order to hold Irish government bonds has spiked dramatically in afternoon trading.
According to Bloomberg figures, yields on 10-year bonds started the day at 7.7%, but at one point shot up to almost 8.5%.
The rates on Irish bonds had come down quite sharply in recent weeks following changes to the EU IMF bailout.
The spike came on the day staff from the European Commission, the European Central Bank and the International Monetary Fund began their latest review of Ireland's bail-out programme.
It is expected that much of the mission will be taken up by discussions related to the preparation of December's Budget, which will be the first for the new Government.
Concentrated action to deal with the banks in the early summer has left Ireland ahead of target in this part of the EU-IMF bail-out plan, but there will be plenty for the Troika team to talk about with the Government.
These include actions to improve competition and the economy and lower costs for consumers, notably action on legal and medical costs.
The Government was supposed to have taken action to remove restrictions on the number of GPs qualifying, and the number of public patients they can take on.
Cutting legal costs and establishing an independent regulator for the legal profession are also conditions for this review, and the Government is expected to publish a Legal Services Bill tomorrow.
The Government is also to report to the troika with a timetable to remove restrictions on large retail units - a move seen as helping to reduce prices.
But most of the discussion will centre on the preparation of December's Budget, and actions to close the deficit to the target of 8.6% of GDP.
Many economists believe this will require an adjustment of more than the €3.6 billion previously agreed to due to lower than expected growth here and abroad.
Troika officials will also examine the results of the comprehensive review of expenditure - the mechanism by which the Government will implement spending cuts over the next three years, and assess progress on additional revenue raising measures such as a property tax.
Kenny to travel to Brussels for Barroso meeting
Taoiseach Enda Kenny is to have a meeting in Brussels this week with the President of the European Commission, Jose Manuel Barroso.
A Government spokesman told RTE News that the meeting on Thursday is being held to discuss challenges facing the euro ahead of the summit of EU leaders later this month.
It is believed Mr Barroso will be holding meetings with other EU leaders separately.
Ministers approve EFSM rate cut
European foreign ministers have formally approved the cut in the interest rate Ireland has to pay for one of the three segments of the bail-out, according to Minister for European Affairs Lucinda Creighton.
Speaking from a meeting of the EU's General Affairs Council in Luxembourg, Minister Creighton said that foreign ministers had formally approved the cut under the European Financial Stability Mechanism, essentially the EU's own community resources, which will save the state several billion euro over a 10-year period.
This is in addition to the interest rate cut under the European Financial Stability Facility, which provides another third of the bail-out and comes from loan guarantees provided by other euro zone governments.
Minister also began the process of formally attaching the Irish guarantees on corporate tax, family and social issues and neutrality to the EU treaties.
The guarantees, which are thought to have helped the previous government win a second Lisbon vote in 2009, are due to be added to European Law in the form of a protocol which will be formally attached when Croatia accedes to the European Union in 2012.
Today's formal adoption by foreign ministers means the guarantees should be agreed by EU heads of government when they meet at the crucial summit on 23 October.
The issue then goes to the European Commission and European Parliament for final approval before the guarantees become a binding part of EU Law.