Europe's biggest economies have agreed to work together to support financial institutions - but without forming a joint bail-out fund.
French President Nicolas Sarkozy hosted the meeting of the leaders of Britain, Germany and Italy in Paris.
They agreed to seek a relaxation of the EU rules governing the amount of money individual states could borrow.
Mr Sarkozy announced a series of other measures - including unspecified action against the executives of failed banks.
Speaking after the meeting at a joint news conference, he said the four had agreed that the leaders of a financial institution that had to be rescued should be "sanctioned".
Mr Sarkozy added: "Each government will operate with its own methods and means, but in a co-ordinated manner."
Leaders were reminded of just how serious the crisis is as talks to rescue Germany's second largest mortgage lender collapsed.
Hypo Real Estate said the 35bn euro (£27.8bn, $51.21bn) deal had fallen apart after the banking consortium involved pulled out. The lender said it would seek to stay in business through "alternative measures".
Meanwhile, Mr Sarkozy suggested EU budget rules - requiring eurozone states to keep their budget deficits below 3% and overall public debt below 60% of gross domestic product - would be adapted to deal with the current "exceptional circumstances".
European Commission President Jose Manuel Barroso agreed that the budget rules would be applied with "flexibility".
European Central Bank chief Jean-Claude Trichet and the chairman of the eurozone group of finance ministers, Jean-Claude Juncker also attended the summit.
The leaders issued a joint call for a G8 summit "as soon as possible" to review the rules governing financial markets.
Ireland reproach
UK Prime Minister Gordon Brown said governments would continue to take measures to ease the credit shortage.
"It has to be indicated to the markets... that European countries will not react as every man for himself"
He said European leaders should send the message that "no sound, solvent bank should be allowed to fail through lack of liquidity".
Mr Brown also won approval at the summit for his proposal for a £12bn EU fund to help keep small businesses afloat during the economic crisis.
German Chancellor Angela Merkel - who said she was not happy with Ireland's action in guaranteeing bank deposits - said each country must act in "a balanced way" that did not cause harm to other EU member states.
"Each country must take its responsibilities at a national level," she said.
'Trial by fire'
The head of the International Monetary Fund (IMF), Dominique Strauss-Kahn, had earlier urged the EU to take co-ordinated action, saying the financial crisis was presenting Europe with a "trial by fire".
No business rush to Irish banks
He held talks with Mr Sarkozy before the EU leaders' meeting and said that although the EU was a more complex organisation than the US, Europe needed to take "concerted collective action".
He said: "It has to be indicated to the markets... that European countries will not react as every man for himself."
He also said he would be scaling back his world economic growth forecasts.
Ahead of the meeting, Germany had made clear its opposition to any co-ordinated European bail-out plan. Mr Brown was also sceptical of the need for any Europe-wide plan.
The president of the European Parliament has criticised the summit, warning that the leaders of Europe's four largest economies have no power to decide for the entire European Union.
Calls for European action follow the bail-out of both Bradford and Bingley in the UK and Fortis Bank by the governments of Belgium, Luxembourg and the Netherlands.
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