French voters have rejected the European Union's proposed constitution in Sunday's referendum, President Jacques Chirac has said.
The vote could deal a fatal blow to the constitution, which needs to be ratified by all 25 members states.
Exit polls published just after voting ended put the "No" side at 55%.
Mr Chirac, who had campaigned hard for a "Yes", accepted the voters' "sovereign decision" - but said France would honour its European commitments.
In his short TV address, he added that the rejection created "a difficult context for the defence of our interests in Europe".
The French leader also said he acknowledged that voters had registered their frustrations in the referendum.
He said he would take a decision on the future of his centre-right government "in the coming days".
Referendum season
There were cheers from supporters of the "No" campaign when the exit polls results were announced just after voting ended at 2200 local time (2000 GMT).
Those who rejected the treaty included Communists, various left-wing groups, dissident socialists and far-right parties.
Foreign Minister Michel Barmier said the vote was a "real disappointment" - but urged other EU countries to go ahead with their own ratification process.
So far nine countries have formally endorsed the constitutional treaty.
Eight other national referendums are still to come, including one in the Netherlands on Wednesday, where the "No" side is also leading in the polls.
The constitution was finalised last year after long and difficult negotiations among EU governments.
The treaty includes the union's Charter of Fundamental Rights and establishes a foreign minister.
Member states can ratify the document through a referendum or by parliamentary vote. Germany ratified it on Friday.