French President Nicolas Sarkozy has said that without ratification of the Lisbon Treaty there can be no further enlargement of the European Union.
He was speaking on French television on the eve of the start of the six-month French Presidency of the European Union.
Commenting on Ireland's rejection of the Treaty, he said that his first priority was to limit the problem to Ireland and that the Czech Republic should ratify the treaty.
He added that when he visits Ireland next month, he would try to find out why Ireland voted no and what could be done to make progress.
However, when asked if Ireland should have a second referendum, the French President said that he did not want to give the impression of forcing Ireland's hand.
However, he noted that there had been a second Irish vote following the rejection of the Nice Treaty.
An umbrella group of anti-Lisbon Treaty campaigners say they will stage a protest in Dublin next month during a visit to Ireland by President Sarkozy.
The group known as the Campaign Against the EU Constitution (CAEUC) represents the left-wing organisations opposed to the Lisbon Treaty including Sinn Féin, People Before Profit and the Socialist Party.
It is concerned that the French presidency of the EU will press ahead with the ratification of the treaty despite its rejection by Ireland.
The group says that Mr Sarkozy needs to respect the rejection of the now defunct EU constitution in France and the Netherlands, as well as the Irish rejection of the treaty.