President Obama has welcomed world leaders to Camp David near Washington for the G8 summit, where the eurozone crisis is likely to dominate talks.

Investors fear a Greek eurozone exit could trigger a fresh global crisis.

At Friday, May 18 opening dinner Iran and North Korea's nuclear ambitions and Syrian unrest were discussed, with broad consensus, officials said.

North Korea faces further isolation, the G8 leaders agreed, if it "continues down the path of provocation".

On Iran, leaders agreed that the onus was on the government in Tehran to prove the claim that its nuclear program was peaceful.

On Syria, a U.S. official said the leaders, including Russia's Prime Minster Dmitry Medvedev, were in agreement that the UN-backed peace plan had yet to be fully implemented and that there was now a need to move towards a political transition.

Earlier, Mr Obama and the new French President, Francois Hollande, made it clear that they wanted a focus on economic growth.

Mr Obama said that tackling the debt crisis in Europe was an issue of extraordinary importance. Greece said that German Chancellor Angela Merkel had suggested on Friday morning that the country could hold a referendum on whether to remain in the eurozone when it votes in national elections next month.

A statement from the office of Greece's interim prime minister said that Mrs Merkel had raised the subject during a telephone call with President Karolos Papoulias.

The German chancellor "conveyed thoughts about a vote parallel to the election with the question to what extent do the Greek citizens wish to remain within the eurozone", said the statement.

The eurozone is expected to top the agenda when the leaders of the US, Germany, France, Britain, Japan, Russia, Italy and Canada hold a full day of talks on Saturday at their annual summit, at President Barack Obama's retreat near Washington DC.

Iran's nuclear program and Syria's crackdown on dissent are also expected to be discussed further, according to BBC News.