China will hold its National People's Congress today, where it is expected to outline possible stimulus measures, but also impose laws to curb tensions in Hong Kong.
US president Donald Trump warned America would respond "very strongly".
"The geopolitical risks are meaningful," BlueBay Asset Management chief investment officer David Riley told Bloomberg TV.
"It's a concern for the market, is a potential source of weakness and a correction."
The S&P 500 was down 0.8%, even as oil rose again.
Gold was sitting at US$1725 an ounce.
The Australian dollar spot price was A$2630/oz as the local currency remained at US65.65c.
The MySteel 62% Australian iron ore fines price dropped 2% to $96 per tonne.
The uranium spot price was slightly higher at $34 a pound.
Copper and zinc fell from multi-month lows.
Nickel rose 0.9% to $12,712/t, the highest level since mid-March.