NEW YORK (AP) -- U.S. stocks fell Monday and markets around the world wobbled as investors continue to question whether they can count on two of the main drivers that propelled markets to record heights: an expanding global economy and low interest rates.
The Standard & Poor's 500 index has whipsawed since setting its all-time high in late January. At first, it was worries that inflation and interest rates may climb higher than the market was anticipating.
Then came last week's surprise promise by President Donald Trump to impose stiff tariffs on imports of steel and aluminum, which investors fear could lead to an escalating trade war that halts a global economy finally growing in sync.
Trump took again to Twitter on Monday to defend the tariffs, which has riled trading partners around the world and already triggered threats of retaliation. Trump highlighted trade deficits with Canada and Mexico, and he said tariffs "will only come off if" a new free-trade agreement between the three countries is signed.
KEEPING SCORE: The S&P 500 index was down 12 points, or 0.5 percent, at 2,678, as of 10 a.m. Eastern time. It's on pace for its fourth drop in the last five days.
The Dow Jones industrial average fell 119, or 0.5 percent, to 24,418, and the Nasdaq composite lost 40, or 0.6 percent, to 7,217.
TRADE WORRIES: White House advisers have fanned out onto television networks in recent days to reject criticism of the proposed tariffs. Trade adviser Peter Navarro said on "Fox and Friends" Monday that there would be no exemptions on the tariffs of 25 percent on steel and 10 percent on aluminum.
Investors have been questioning whether Trump's initial promise would prove to be just an opening bid in negotiations, with the actual move being less consequential. Stocks pared sharp losses on Friday amid such speculation.
If a trade war does happen, it could put profits for big U.S. companies at risk because they are heavily reliant on the global economy. Companies in the S&P 500 got 43 percent of their sales from outside the United States in 2016, according to S&P Dow Jones Indices. If countries throw up barriers blocking U.S. companies from those customers, it would undercut what had been encouraging sales growth.
MIXED GLOBAL MARKETS: European markets were mixed following elections in Italy that saw no single party emerge with a majority in Parliament. That raises uncertainty about how closely Italy will work with the rest of the European Union.
Italian stocks fell, but markets elsewhere on the continent were mixed. France's CAC 40 flipped between modest gains and losses. Germany's DAX rose 0.7 percent, and the FTSE 100 was up 0.1 percent in London.
In Asia, Japan's Nikkei 225 fell 0.7 percent, South Korea's Kospi dropped 1.1 percent and the Hang Seng in Hong Kong lost 2.3 percent.
Stocks in Shanghai edged up after Beijing set an annual growth target for the world's No. 2 economy of "around 6.5 percent" for 2018. That's down from 6.9 percent last year, but still robust. Premier Li Keqiang also outlined plans to forge ahead with an overhaul of state industry, ramp up military spending and pursue advanced technology.
COMMODITIES: Benchmark U.S. crude rose 12 cents to $61.37 per barrel. Brent crude, the international standard, rose 6 cents to $64.43 a barrel.
Gold fell $2.00 to $1,321.40 per ounce.
YIELDS: The yield on the 10-year Treasury fell to 2.84 percent from 2.87 percent late Friday.
CURRENCIES: The dollar rose to 105.79 Japanese yen from 105.54 yen late Friday. The euro dipped to $1.2323 from $1.2331, and the British pound climbed to $1.3820 from $1.3790.