"We have an agreement on treaty amendment," President of the European Council Herman Van Rompuy said on his twitter posting.

"The member states whose currency is the euro may establish a stability mechanism to be activated if indispensable to safeguard the stability of the euro area as a whole. The granting of any required financial assistance under the mechanism will be made subject to strict conditionality," the agreement said.

The EU leaders agreed to introduce "limited change" to the Lisbon treaty at their autumn summit under the strong call from Germany and mandated Van Rompuy to put forward proposals for the amendment.

After the Greece debt crisis, the EU put together with the International Monetary Fund (IMF) a 750-billion-euro rescue fund to bail out countries which may fall prey to the debt crisis. But the mechanism will expire in 2013.

Germany, the largest contributor to the rescue fund, has argued that the rescue fund is against the so-called non-bailout clause of the Lisbon treaty and called for change of the treaty to lay a solid foundation for future permanent rescue mechanism.

The leaders also outlined the permanent rescue mechanism at the meeting.