By Marc JonesLONDON (Reuters) - Credit rating firm Moody's cut its 2016 global economic growth forecasts on Friday, with China and United States both trimmed and Russia and Brazil seen staying in recession.It was a surprise move from the firm, coming just 10 days since its last forecasts. It put average growth in the top 20 world economies at 2.8 percent on average, versus the 3 percent it had forecast previously.It said the fresh cut reflected information that had become available since the earlier forecasts were published.China, Japan and Korea's growth saw downgrades partly due to expectations of more muted exports. Emerging markets Turkey and South Africa had their forecasts reduced too."The (China) policy stimulus measures that have been implemented have been broader-ranging and larger than we had expected. This suggests that the underlying economic environment is weaker than we previously thought," the report said."We have revised our U.S. 2016 forecast down slightly as the negative impact of the stronger dollar seems more pronounced than we assumed previously," it said cutting it to 2.6 percent from 2.8 percent.It kept its euro zone forecast unchanged despite the recent turbulence in Greece, at 1 and 2 percent in 2015 and 2016.It said Brazil's output would shrink as much as 1 percent in 2016 and Russia's as much as 1.5 percent."The price of many globally-traded commodities has fallen very sharply in the last 18 months. The slowdown in China, a major consumer of commodities, will continue to weigh on prices," Moody's said.(Reporting by Marc Jones; editing by Andrew Roche)Join the conversation about this story »