Nine of the EU's poorer eastern member countries said they could not afford to give billions of euros to developing countries to fight the effects of global warming, with Hungary and Poland demanding that richer EU states pay a larger share of the costs.
"The burden-sharing proposal is not acceptable in its current form," Hungarian Prime Minister Gordon Bajnai said.
Swedish Prime Minister Fredrik Reinfeldt, chairing the Brussels summit, said the bloc's integrity was on the line. An EU commitment would signal to the United States, Japan and other top donors that they must also make substantial aid pledges, he said.
Reinfeldt added that if the talks end without a clear financial commitment, a United Nations climate change conference in Copenhagen Dec. 7-18 could be jeopardized.
"We are very close to the Copenhagen conference. This is the time to form our mandate," EUobserver.com quoted Reinfeldt as saying before the summit began.
He added, "We stand before a very complicated summit meeting."
Besides funding to slow global warming, the leaders seek to remove obstacles to the 2007 Lisbon Treaty, which aims to streamline decision-making and reform the bloc's structures.
The treaty, which would also create a full-time EU president, must still be ratified by Poland and the Czech Republic.