(REUTERS) -- EU leaders reached agreement at a summit on Monday on the introduction of a permanent euro zone bailout mechanism from July 2012, with a treaty governing the fund to be signed at a later date, three EU officials told Reuters.

The European Stability Mechanism, which will have a lending capacity of 500 billion euros, will take over from the European Financial Stability Facility, a temporary mechanism that has so far been used to bail out Ireland and Portugal.

There is a deal but the treaty will be signed at a later stage, one EU official said. Two other EU officials confirmed the news.

The ESM was originally expected to come into force in July 2013, but Germany pushed for an earlier introduction so that a more stable, permanent fund with paid-in capital could be set up, building a stronger firewall against the debt crisis.