WASHINGTON (Reuters) - The International Monetary Fund warned on Thursday it will likely cut its growth forecasts for the United States and the global economy if automatic U.S. spending cuts take effect on Friday.

IMF spokesman William Murray said the IMF would likely shave the 2013 U.S. growth forecast by at least 0.5 percentage point if the cuts are fully implemented. The IMF is currently projecting the U.S. economy will expand 2 percent this year.

He said the United States' biggest trading partners are likely to be most affected by the impact from the so-called sequester.

"We will see what happens on Friday, but everybody is assuming that sequestration is going to take effect," Murray told a regular news briefing. "What it means is that we are going to have to reevaluate our growth forecasts for the United States and other forecasts," he added.

(Reporting by Lesley Wroughton; Editing by James Dalgleish)