The Czech PM said he would not bet much on a Czech 'Yes'
EU leaders have admitted that the Czech Republic may not be able to ratify the Lisbon Treaty, which has already been rejected by the Irish.
The declaration from their summit in Brussels notes that the Czech process is on hold due to legal difficulties.
But they said ratification would continue elsewhere, and ruled out renegotiation of the treaty.
But British PM Gordon Brown said the UK could not definitively ratify it until a court ruled on a legal challenge.
It followed a warning from a judge in the case that ratification should be delayed until the ruling was in.
The treaty passed through British parliament this week, but has still to complete formal ratification.
Mr Brown said the judge's intervention would not affect the process, which would not have been completed until after the court judgement anyway.
The Brussels summit has been overshadowed by the Irish result, despite efforts to concentrate on food and fuel prices, and now the Czech threat hangs over the treaty.
The EU declaration noted that: "The Czech Republic cannot complete their ratification process until the constitutional court delivers its positive opinion on the accordance of the Lisbon Treaty with the Czech constitutional order".
The Czech parliament's ratification was suspended after the Senate demanded that the court rule on its constitutionality.
The Czech Prime Minister Mirek Topolanek said at the summit that he was not going to try to halt the ratification process in his country.
But he added: "I am not going to force MPs to back Lisbon and I wouldn't bet 100 crowns (£3, $6) on a Czech 'Yes'."
The Czech President, Vaclav Klaus, said after the Irish vote that it had killed off the treaty.
With growing opposition from Euro-sceptics, and key elections due in October, the future of the treaty in the Czech Republic looks uncertain, says the BBC's Oana Lungescu at the summit in Brussels.
'Not just for fun'
The issue has obstructed attempts to get a common position in Brussels - that ratification should continue, while the Irish government takes time to consider its next step.
But President Sarkozy said EU leaders had decided that: "The treaty ratification process should continue in all member states, that's the position now of the council."
LISBON TREATY PROGRESS
Approved by parliament: Austria, Bulgaria, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Latvia, Lithuania, Luxembourg, Malta, Poland, Portugal, Romania, Slovakia, Slovenia, UK
Defeated by referendum: Irish Republic
Challenges: Legal objections in Czech Republic, UK
No firm date: Belgium, Cyprus, Netherlands (held up by referendum proposal), Italy (new government), Spain (new government), Sweden
"Ireland is a problem, but if we have a second or third problem then it's really going to get difficult," he added.
The treaty must be ratified by all 27 member states to take effect. Nineteen have approved it so far.
European Commission President Jose Manuel Barroso ruled out renegotiating the reform treaty.
"When a treaty is signed by 27 governments it's not just for fun," he said. "It's inconceivable that a government signs a treaty without the intention of ratifying it. It's a principle of international law."
Mr Sarkozy and German Chancellor Angela Merkel said the European Union would not be able to expand further without ratification of the Lisbon Treaty, in what correspondents said appeared to be an attempt to lean on the Czechs, as well as Poland, who are keen on eastward expansion.
Polish Prime Minister Donald Tusk rejected that stance as "unacceptable".
Friday's declaration made reference to several other matters, not least the soaring fuel and food prices that have hit consumers and sparked protests across Europe.
- said the EU Commission should by October "examine the feasibility of taxation measures to smooth the impact of sudden oil price increases"
- threatened tougher sanctions against Zimbabwe amid pre-election violence
- threatened tougher sanctions against Sudan over its refusal to hand over officials wanted for war crimes in Darfur
- delayed a decision on a date for Macedonia to start accession talks with the EU
- agreed to scrap diplomatic sanctions against Cuba imposed in 2003