EU leaders have reached a deal on helping Greece tackle its debt crisis, EU President Herman Van Rompuy says.

He gave no further details, but all 27 EU leaders are now set to discuss it, BBC reported on Thursday.

German Chancellor Angela Merkel said Greece "will not be left on its own, but there are rules and these rules must be adhered to".

Greece's debt crisis has put pressure on the euro, and it will dominate the EU summit now under way in Brussels.

There was an instant reaction on the markets, where traders welcomed news of the deal. Major European markets rebounded from earlier falls and the euro rose against the US dollar.

Van Rompuy, the new President of the European Council, said the 16 eurozone countries "will take determined and coordinated action if needed to safeguard stability in the eurozone as a whole".

He also stressed that Greece had not asked for financial aid, and added that the EU was expecting "rigorous" action from the Greek government.

It is the first big test for Van Rompuy, who wanted the summit to focus on a new strategy for jobs and growth - a blueprint for the next 10 years. But defending the euro is now a more pressing issue.

EU rules prevent the eurozone from collectively bailing out Greece, but the debt crisis has forced EU leaders to seek ways to help nevertheless.

Greece's deficit is, at 12.7%, more than four times higher than eurozone rules allow. For years Greek spending has ballooned while tax revenue has diminished.

Its debt is about 300bn euros ($419bn), and the government estimates it will need to borrow about EUR53bn this year to cover budget shortfalls.

Debt servicing is now costing Greece 11.6% of its gross domestic product and it has to pay more interest on loans now because its credit rating has been downgraded.