The presidents of the European Commission and European Council both arrived in St. Petersburg on Thursday (September 5), just hours before the Group of Twenty summit was due to officially kick off.
They will be attending the two-day summit which will be held at a tsarist palace outside St. Petersburg and which looks set to be dominated by the crisis in Syria.
A potential showdown over the issue between U.S. President Barack Obama and Russia's Vladimir Putin could overshadow the meeting of world leaders which is normally aimed at how to revive the global economy.
The Group of 20 developed and developing economies will try to forge a united front on growth, trade, banking transparency and fighting tax evasion.
The club that accounts for two-thirds of the world's population and 90 percent of its output is divided over issues such as emerging markets turmoil and the Federal Reserve's decision to end its programme of stimulus for the U.S. economy.
But no rift is wider than the one between Obama and Putin over possible military intervention in Syria.
Presented by Adam Justice