The move is seen as part of Ukraine's efforts to reinforce its army as soldiers struggle to hold positions against Russia
The IMF is forecasting world growth this year of 3.9 percent, down from an estimate of 4.1 percent in its World Economic Outlook last month, said the official, who is involved in planning for the meeting and spoke on condition of anonymity.
It forecasts 2009 growth of 3.7 percent, down from 3.9 percent.
The IMF report said the world economy would slow further in the second half of the year, the source said.
"Commodity prices will remain high and volatile" and "market turbulence will go on through 2009", the source said.
The IMF left unchanged its forecast for U.S. growth this year at 1.3 percent, said the official. It shaved its forecast for 2009 U.S. growth to 0.7 percent from 0.8 percent.
The IMF trimmed its forecast for euro zone growth this year to 1.4 percent from 1.7 percent in July. It estimated 2009 growth at 0.9 percent, down from 1.2 percent.
The euro zone's economy shrank 0.2 percent in the second quarter compared with the previous three months, the first contraction since the reporting series began in 1995, the European Union's statists office, Eurostat, said on Aug. 14.
Deputy finance ministers from the G20, a group of emerging and industrialised economies, will meet on Saturday and Sunday in Rio de Janeiro.
The move is seen as part of Ukraine's efforts to reinforce its army as soldiers struggle to hold positions against Russia
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