The International Monetary Fund cut its global outlook for this year and next as capital outflows further weaken emerging markets and warned that a U.S. government default could "seriously damage" the world economy.

Growth worldwide will be 2.9 percent this year and 3.6 percent next year, the IMF said in a report released today in Washington, compared with July predictions of 3.1 percent for 2013 and 3.8 percent for 2014. It sees emerging economies growing 4.5 percent this year, 0.5 percentage point less than three months ago, as projections were reduced for China, Mexico, India and Russia.

"Advanced economies are gradually strengthening" while "growth in emerging-market economies has slowed," IMF chief economist Olivier Blanchard wrote in a foreword to the World Economic Outlook report. "This confluence is leading to tensions, with emerging-market economies facing the dual challenges of slowing growth and tighter global financial conditions."