US stocks eased overnight and the S&P 500 closed below a key technical level for the first time since Election Day, pressured by lingering geopolitical concerns and President Donald Trump's comments on the US dollar and interest rates.

Trump said in a Wall Street Journal interview that the US dollar "was getting too strong" and that he would like to see interest rates stay low (see previous post). The US dollar, which has risen along with prospects for higher rates, hurts profits at US multinationals when it strengthens.

"Markets don't like uncertainty," said Peter Tuz, president of Chase Investment Counsel. "This just kind of added another wild card into the mix in a way, whether there will be actions taken to keep the dollar from strengthening further."

Investors sought shelter in defensive shares and other low-risk assets. Industrials and materials were the biggest drags on the market along with financials, while utilities, staples and telecommunications gave the S&P 500 its biggest lift.

The S&P financial index was down 0.9 per cent a day ahead of results from three major banks in what will mark the start of the corporate earnings season. Analysts are expecting earnings to have risen 10 per cent for all S&P 500 companies in the first quarter.

The materials and industrials indexes both ended more than 1 per cent lower on the day.

In a sign that further weakness may be ahead, the S&P 500 closed below its 50-day moving average for the first time since November 8. The CBOE Volatility index, Wall Street's fear gauge, extended recent gains, a day after it closed above 15 for the first time since the election.

Rising US tensions with Russia, North Korea and Syria after US missile strikes in Syria last week and the moving of US warships toward the Korean Peninsula have kept investors cautious.

The Dow Jones Industrial Average closed down 59.44 points, or 0.3 per cent, to 20,591.86, the S&P 500 lost 8.85 points, or 0.38 per cent, to 2,344.93 and the Nasdaq Composite dropped 30.61 points, or 0.52 per cent, to 5,836.16.

Investors are concerned these developments could distract Trump from pursuing pro-business policies such as tax cuts, simpler regulations and higher infrastructure spending, promises that have powered Wall Street to record highs since his election in November.

Wells Fargo, Citi and JPMorgan are due to report results on Thursday, the last trading day of the week ahead of the Good Friday holiday.