Ireland's voters have dealt the European Union a stunning diplomatic setback by rejecting its blueprint for reform in referendum results announced Friday.

The Irish government was the only member of the 27-nation EU required by its own constitution to put the Treaty of Lisbon to a popular vote — and was left reeling when 53.4 percent of voters rejected the 260-page document in Thursday's referendum.

Irish Prime Minister Brian Cowen said he respected the voters' verdict — but sidestepped reporters' questions as to whether the treaty was now dead.

"I wish to make it clear to our European partners that Ireland has absolutely no wish to halt the progress of a union which has been the greatest force for peace and prosperity in the history of Europe," said Cowen, who faces potential isolation and embarrassment at an EU summit next week.

Voters cited myriad fears over the rapid growth and ambitions of the EU. Anti-treaty groups from the far left and right mobilized "No" voters by claiming that the treaty would empower EU chiefs in Brussels, Belgium, to force Ireland to change core policies — including its low business tax rates, its military neutrality and its ban on abortion.

"This is a very clear and loud voice that has been sent yet again by citizens of Europe rejecting the antidemocratic nature of Brussels governance," said Declan Ganley, leader of Libertas, the most prominent anti-treaty campaign group in Ireland.

While Cowen stressed the need to keep Irish diplomatic options open, others in his government emphasized that Ireland faced diplomatic isolation because it could not ask people to vote again on essentially the same thing.

Ireland's minister for European affairs, Dick Roche, said Ireland was constitutionally barred from passing the treaty now. He forecast it would be difficult, if not impossible, for EU leaders to find a solution that would permit a second Irish referendum.

"As far as I'm concerned, this treaty is a dead letter," Roche said, adding that Ireland's voters have "made life very difficult for us going out to Brussels. We are in completely uncharted territory here, a very strange position."

The treaty seeks to create more powerful positions of EU president and foreign policy chief, reduce the policy areas that require unanimous support from members, and give the European Parliament more say in scrutinizing policies. Most proposals were originally contained in the EU's aborted constitution, which French and Dutch voters shot down in 2005.

In the EU's power base of Brussels and other European capitals, leaders vowed to complete ratification of the Lisbon treaty through the governments of the other 26 members — even though, legally, the treaty cannot come into force because of the Irish rejection.

"At the European Council, we will want to confer with each other, to hear Prime Minister Cowen's analysis, as well as his ideas on how to address the concerns expressed by those who chose to vote no," EU President Jose Manuel Barroso told reporters in Brussels.

In neighboring Britain, one of eight EU partners yet to ratify the treaty through their parliaments, Foreign Secretary David Miliband said the Irish outcome "needs to be respected and digested" — but should not oblige other countries to postpone their own ratification plans.

"I think it's important that no ones tells them what to do next. It's very important that the Irish make their own decisions about how to go forward on the basis of a careful analysis of the results," Miliband said.

German Chancellor Angela Merkel agreed that patient diplomacy might eventually turn the Irish "No" to a future "Yes."

"We would have liked a different outcome, but as good Europeans we now have the task of simply taking the situation as it is and finding a way out, while at the same time respecting the vote of the Irish," she said.

Ireland did vote against the EU's Treaty of Nice in 2001, creating a similar diplomatic crisis. That was resolved when EU chiefs approved an Irish amendment emphasizing Ireland's continued neutrality, which the Irish government used as an excuse to mount a 2002 referendum backed by a much stronger campaign.

But on that occasion, the Irish government emphasized that the 2001 vote lacked democratic credibility because of its paltry 34.8 percent voter turnout. Thursday's referendum, by contrast, mobilized more than half of all registered voters — an unusually strong turnout by Irish standards.

Anti-EU activists said voters clearly do not trust their political elites, whether in Dublin or Brussels.

Anti-treaty campaigners jubilantly chanted "No!" as they drowned out Finance Minister Brian Lenihan at the major ballot-counting center in Dublin. Lenihan struggled to speak to reporters, then gave up and walked out, as one activist waved a sign reading "No to foreign rule" over his head.

The outcome appears likely to fuel populist cries across the continent for more democratic accountability within the EU, which has long struggled from its Brussels base to connect with its nearly 500 million citizens.

"This is a huge rebuff to the political establishment. It shows there is massive distrust among ordinary working people," said Joe Higgins, the sole Socialist Party member in the Irish parliament.

Rural and working-class areas were almost universally anti-treaty, whereas better-off parts of Dublin registered stronger support for the EU. In suburban south Dublin, a largely wealthy and highly educated district, the "Yes" camp triumphed with 63 percent of the vote. But a neighboring, scruffier district voted 65 percent "No."

The euro common currency fell to a one-month low on news of the Irish result.

Ireland views itself as a pro-EU state that has broadly benefited from 35 years of membership. Yet even here, a majority of voters appeared determined to register their opposition to the growth of a continental government that would erode Ireland's sense of independence.

"People felt a convincing case for the treaty had not been made, and they felt hectored and bullied into supporting it while the wool was being pulled over their eyes," said Richard Boyd Barrett, leader of a hard-left pressure group called People Before Profit.