Under pressure to prevent a catastrophic breakup of their single currency, euro zone leaders agreed on Friday to let their rescue fund inject aid directly into stricken banks from next year and intervene on bond markets to support troubled member states.
They also pledged to create a single banking supervisor for euro zone banks based around the European Central Bank in a landmark first step towards a European banking union that could help shore up struggling member Spain.
"It is a first step to break the vicious circle between banks and sovereigns," European Council President Herman Van Rompuy told a final news conference after talks which stretched right through the night.
The deal was widely seen as a political victory for embattled Italian Prime Minister Mario Monti and his Spanish counterpart, Mariano Rajoy, over German Chancellor Angela Merkel, who had brushed aside any need for such emergency measures earlier this week.
ECB President Mario Draghi endorsed the "tangible results", which sent the euro nearly 2 percent higher and sharply cut Spanish and Italian bond yields. European shares rose, led by banking stocks buoyed by the prospect of moves to backstop the financial system.
"I am actually quite pleased with the outcome of the European Council. It showed the long-term commitment to the euro by all member states of the euro area," Draghi told reporters.
Market participants welcomed the outcome as a substantial step to restore confidence in the 17-nation euro zone, which was saluted by a more durable rally than previous summit outcomes.
"It's inching closer to a banking union, and the closer we get to a banking union would put (the EU) well on the road to a fiscal union," said Art Hogan, managing director of Lazard Capital Markets in New York.
Most economists polled by Reuters expect the ECB to cut borrowing costs at its July 5 meeting, which takes place against a darkening economic backdrop. But internal resistance to the central bank reviving its bond-buying program remains high.
After 14 hours of tense talks that ended at 4:30 a.m. (0230 GMT), the 17 leaders agreed on a series of short-term steps to shore up their monetary union and bring down the borrowing costs of Spain and Italy, seen as too big to bail out.
To that end the euro zone's temporary EFSF and permanent ESM rescue funds will be used "in a flexible and efficient manner in order to stabilize markets" to support countries that comply with EU budget policy recommendations, a joint statement said.
It gave few specifics, but euro zone officials said the funds could buy bonds on both the primary and secondary markets on the basis of a memorandum of understanding signed with the requesting state and up to a funding limit to be agreed.
Both Italy and Spain said they did not intend to call on that mechanism to stabilize markets for now, hoping the Brussels agreement will serve as a sufficient deterrent.
Washington said it was encouraged by the progress but White House press secretary Jay Carney told reporters travelling with President Barack Obama that "a lot of details" still needed to be worked out, and the euro zone was likely to need to take further steps in the future.
The International Monetary Fund said the summit had taken "the right steps toward completing monetary union" while ratings agency Fitch said the deal eased near-term pressure on euro zone sovereign ratings.
BRUSSELS (Reuters)