International political tensions, tight energy markets and a possible American economic slowdown towards 2007 will cast a cloud over financial markets this year, George Soros, the billionaire investor, said today.

Speaking at the World Economic Forum, Mr Soros argued that "an unexpectedly strong decline in America’s influence in the world" had contributed to the crisis over Iran’s nuclear ambitions, underpinning high oil prices.

"I see the Iranian crisis slowly maturing, and usually political developments don’t affect markets very much, but in this case they may," he said.

He added: "2006 is a dangerous year as far as oil is concerned."

High oil prices could prompt Ben Bernanke, the incoming chairman of the US Federal Reserve, to pursue further interest rate tightening this year, and Mr Soros forecast at least one more increase.

"He also has to establish his credibility" as an inflation hawk with markets to meet a standard set by Alan Greenspan over his 18-year term as Fed chairman.

That would contribute to a slowdown in the surging American housing market, Mr Soros said, and households which have driven US economic growth in recent years would begin to spend less.

"As the housing boom cools off, the savings rate is likely to rise, and that will lead to a shortfall in demand that I think will bring a global slowdown," he said.

"I expect a slowdown in 2007, which will probably cast its shadow over the markets in 2006."

The dollar might not suffer from a slump immediately however, because higher US interest rates than in Europe or Japan would continue to attract foreign capital, he added.

He said: "That doesn’t mean that the dollar is about to fall out of bed, because the interest rate differential is still there, and it may still be rising."