This week's G20 summit will require every bit of President Barack Obama's diplomacy skills after the Federal Reserve embarked on a new US$600 billion bond-buying spree, sparking criticism from four continents that the US central bank was ignoring the global repercussions.

Officials from Germany, Brazil, China and South Africa were among those expressing concern that the Fed's money printing could weaken the dollar, drive up commodity prices and send uncontrollable waves of investor cash into emerging markets.

If the G20 fails to defuse these global tensions, it may heighten investor concerns that policymakers are drifting further apart, leaving the world economy vulnerable to another bout of upheaval.

Domestic politics and policies make Obama's job tougher. He arrives in Seoul for the November 11-12 summit weakened by a crushing congressional election defeat for his Democratic Party. His primary task will be to convince his peers the Fed's actions do not run counter to a U.S.-led push for global cooperation to even out economic imbalances.

It was less than five months ago that G20 leaders gathered in Toronto, talking in warm and fuzzy terms about "collective well-being" and "shared objectives."

"G20 members have a responsibility to the community of nations to assure the overall health of the global economy," the leaders said in their closing statement in June.