NEW YORK (AFP) - Wall Street stocks fell for the second straight session on Wednesday (Aug 9) as worries about US-North Korea tensions rattled investors.

Analysts pointed to the harsh threats and sabre rattling from US President Donald Trump, including a message Wednesday on Twitter boasting the United States' nuclear arsenal was now "more powerful than ever before."

US Defence Secretary Jim Mattis, who often has emphasised the devastating costs of any conflict with North Korea, seemed to back up Trump's tone.

Mattis said North Korea must stop isolating itself and "stand down" in its pursuit of nuclear weapons, and Pyongyang "should cease any consideration of actions that would lead to the end of its regime and the destruction of its people."

The Dow Jones Industrial Average shed 0.2 per cent to close the day at 22,048.70.

The broad-based S&P 500 fell less than 0.1 per cent at end at 2,474.02, while the tech-rich Nasdaq Composite Index dropped 0.3 per cent to 6,352.33.

The S&P 500 volatility index, a measure of investor fear, rose for a second day.

"It is a market that is beginning to encounter some major threats and of course the threat is geopolitical," said Peter Cardillo, chief market economist at First Standard Financial.

Dow member Disney dropped 3.9 per cent as it reported flat third-quarter revenues due in part to weakness in its cable subscription business.

Disney also announced it will launch two new streaming television services including one for its ESPN-branded sports channel, while ending its deal with Netflix as it shifts towards direct content distribution. Netflix lost 1.5 per cent.

Priceline sank 6.9 per cent as it projected third-quarter earnings below analyst expectations.

Charter Communications rose 2.9 per cent on news Altice is exploring a bid for the cable giant. Altice USA, the subsidiary of the French company, added 0.1 per cent.