Voters in Ireland are casting ballots Thursday in a referendum on the European Union's new reform treaty.

The vote is being closely watched by EU leaders after opinion polls showed the outcome was too close to call.

The treaty would reform EU institutions, streamline the decision-making process, and give greater powers to the EU president and foreign policy chief.

The governments of all European Union members must approve the treaty. Ireland is the only country is holding a national vote on the treaty.

On Wednesday, the parliaments of Greece, Finland, and Estonia ratified the treaty, bringing the number of countries that have approved it to 18.

In the run up to the vote Irish Prime Minister Brian Cowen urged voters to support the measure and stressed that the country must not give the impression of turning its back on Europe.

Opponents say a "yes" vote will undermine Ireland's current prosperity by imposing EU-wide measures such as changing the tax system.

The treaty is a revised version of the draft EU constitution, which failed in 2005 when French and Dutch voters rejected it.

Some information for this report was provided by AFP and AP.