NEW YORK (AFP) - Wall Street stocks finished a choppy day little changed as investors weighed how seriously to take increasingly heated rhetoric between US President Donald Trump and North Korea's Kim Jong Un.

Trump, who threatened earlier this week to "totally destroy" North Korea, went after the country's leader again Friday on Twitter calling him a "madman" who "will be tested like never before!"

Earlier, Kim called the Trump a "mentally deranged US dotard" after the reclusive regime hinted it may explode a hydrogen bomb over the Pacific Ocean.

US stocks opened lower but two of the three major indices finished the day with modest gains.

"The markets no longer pay attention to what Trump says," said Gregori Volokhine, president of Meeschaert Capital Markets. "They're waiting to see what Trump does."

The Dow Jones Industrial Average slipped 0.1 per cent to end the week at 22,349.59.

The broad-based S&P 500 added 0.1 per cent to 2,502.22, as did the tech-rich Nasdaq Composite Index which closed at 6,426.92.

Apple fell 1 per cent as its latest smartphone, the iPhone 8, arrived in stores. Some analysts think sales of the device will be weak due to the impending introduction of the even more richly endowed iPhone X, which will hit shelves in November.

Others to fall included Tesla Motors, which shed 4.2 per cent, and Kraft Heinz, which lost 1.9 per cent.

Embattled consumer credit scoring company Equifax gained 6.9 per cent following an upgrade from Wells Fargo.

Texas Instruments won 2.6 percent after announcing that it boosted its dividend by 24 per cent authorised an additional US$6 billion in share repurchases.

Sprint jumped 6.1 per cent and T-Mobile US rose 1.1 per cent following reports the cellphone providers are close to a deal to merge. Other telecom companies also were strong, with Verizon advancing 2 per cent and AT&T 1 per cent.