About 15 minutes into trading, the Dow Jones Industrial Average was down 0.1 percent to 25,302.23.

The broad-based S&P 500 was up slightly at 2,738.73, while the tech-rich Nasdaq Composite Index advanced less than 0.1 percent to 7,276.20.

Much intrigue surrounding Saudi Arabia, Russia and Britain, among others, hangs over the G-20 gathering in Buenos Aires. But the biggest question for investors is whether US President Donald Trump can hash out a trade deal with President Xi Jinping when the two dine on Saturday.

"This market remains as malleable as ever when it comes to hopeful-sounding rhetoric on trade developments from leading officials," said Briefing.com analyst Patrick O'Hare.

"In the end, it will be the comments from President Trump and President Xi after the dinner meeting that dictate the market's near-term direction."

Among individual companies, hotel chain Marriott International slumped 5.2 percent after announcing that it suffered a hack of up to 500 million guests from the reservation database of the Starwood, which the company acquired in 2016.

General Electric fell 4.3 percent after a Wall Street Journal report described a deepening US probe into accounting at the slumping conglomerate. The article quoted one former employee who left the company out of concern that senior executives were not accounting for risk in an insurance division that later suffered a $15 billion shortfall.