The precious metal, a traditional safehaven store of value in troubled times, reached $1,497.23 an ounce on the London Bullion Market, before easing back.
S&P "has caused consternation in almost every asset class from currencies to commodities to indices," said Ian O'Sullivan, analyst at trading group Spread Co.
US stocks opened sharply lower after the ratings agency issued the warning on US sovereign debt, citing Washington's huge debt and fiscal deficit.
