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All three key US share indexes are still trading in negative territory.

The Dow Jones is at 21,817.95, that's a fall of 82 points or 0.37%.

The S&P 500 is at 2,442.77, 10 points or 0.40% lower.

And the Nasdaq is at 6,268.39, down 29 points or 0.46%.

The fall comes after President Donald Trump Donald Trump said he would close down the US government if necessary to build his wall along the Mexico border.

He said that, if it came to it, he would risk a government shutdown - which is what happens when legislation funding the federal government cannot be passed by Congress and non-essential services stop.

"Trump saying he would be willing to shut down the government over the wall obviously doesn't really inspire much confidence in anyone," said Michael O'Rourke, chief market strategist at JonesTrading.

"The debt limit, which is truly urgent and something that needs to be addressed, where theoretically failure should not be an option, that is something of a litmus test for the market."