"It is a reflexive bid," Briefing.com's Patrick O'Hare said of the early gains. "Market participants will presumably want to test the conviction of the buy-the-dip crowd to see if there is more to the mechanical rebound trade than meets the cynical eye."

About 10 minutes into trading, the Dow Jones Industrial Average was up 0.1 percent at 34,338,95.

The broad-based S&P 500 advanced 0.3 percent to 4,364.52, while the tech-rich Nasdaq Composite Index advanced 0.5 percent to 14,614.88.

The S&P 500 lost two percent on Tuesday amid worries over rising Treasury yields and the impasse in Congress over raising the debt ceiling.

The lack of progress in Washington on a deal has raised the possibility of a default on US government debt, while lawmakers must also reach an agreement on funding the government this week to prevent a shutdown.

Policy makers such as Treasury Secretary Janet Yellen have warned of dire consequences from failing to raise the borrowing limit.

The market has so far taken the risk in stride, with many investors pointing to a history of brinksmanship prior to last-minute agreements that avert a default.