NEW YORK (CNNMoney) -- U.S. Treasury Secretary Tim Geithner warned Saturday that the sovereign debt and banking crisis in Europe represents "the most serious risk now confronting the world economy." In an official statement to the International Monetary Fund, Geithner also discussed the need to both support the U.S. economy in the short term and take steps to lower the nation's long-term deficits. But his strongest comments were directed at Europe, where the specter of a default by the Greek government has upset financial markets around the world. The nation's long-standing debt problems are threatening to spill over into the European banking system, with possible repercussions for the fragile U.S. economy. While he praised the actions European leaders have taken so far, Geithner said more needs to be done to create a "firewall against further contagion." http://money.cnn.com/2011/09/24/markets/geithner_debt/index.htm?hpt=hp_t1 "The threat of cascading default, bank runs, and catastrophic risk must be taken off the table, as otherwise it will undermine all other efforts, both within Europe and globally," the Treasury chief said. "Decisions as to how to conclusively address the region's problems cannot wait until the crisis gets more severe." Geithner also reiterated his argument that President Obama's recently proposed $447 billion plan to boost hiring and employment could create one million jobs "at a critical moment in the recovery." At the same time, Geithner reaffirmed the administration's commitment to reduce deficits by more than $3 trillion over 10 years by cutting spending and reforming the nation's tax code.