Exxon's 1.56 percent rise was the biggest boost on the S&P, while Goldman Sachs and Home Depot's more than 1 percent rise propelled the Dow.

"I think it (North Korea) is still going to be a factor with a bit of nervousness out there. We also have another hurricane heading towards Florida," said Scott Brown, chief economist at Raymond James in St. Petersburg, Florida. "We're already seeing water flying off the shelves at grocery stores."

North Korea conducted its most powerful nuclear test yet on Sunday, triggering a dramatic escalation of its stand-off with the United States that drove investors towards safe-haven assets.

Also weighing on investors' mind is Hurricane Irma, which is en route to a possible Florida landfall at the weekend.

At 9:39 a.m. ET (1339 GMT), the Dow Jones Industrial Average was up 65.91 points, or 0.3 percent, at 21,819.22 and the S&P 500 was up 5.84 points, or 0.24 percent, at 2,463.69.

The Nasdaq Composite was up 10.73 points, or 0.17 percent, at 6,386.30.

All the 11 major S&P indexes were higher, with a 0.67 percent rise in the energy index topping the advancers.

Oil prices rose on Wednesday as strong global refining margins and the reopening of U.S. Gulf Coast refineries provided a more bullish outlook after sharp drops due to Storm Harvey.

Financial stocks also gained 0.55 percent, a day after they suffered their biggest one-day fall since mid-May.

The Federal Reserve issues its Beige Book, a round-up of anecdotes on the health of the economy, at 02:00 p.m. E.T.

Three Fed policymakers on Tuesday expressed doubts about further rate hikes, with one influential policymaker calling for a delay in raising U.S. interest rates until the Fed is confident inflation will rebound.

Data showed the U.S. trade deficit increased less than expected in July as both exports and imports fell, suggesting that trade could contribute to economic growth in the third quarter.

The Commerce Department said the trade gap rose 0.3 percent to $43.7 billion, compared with an increase to $44.6 billion forecast by economists polled by Reuters.

Newell Brands was off more than 4 percent after the company slashed its profit outlook for 2017.

Sarepta Therapeutics was up about 12 percent after its drug to treat patients with a form of Duchenne Muscular Dystrophy met the main goal in an early-stage study.

Advancing issues outnumbered decliners on the NYSE by 1,800 to 691. On the Nasdaq, 1,455 issues rose and 819 fell. (Reporting by Sruthi Shankar in Bengaluru; Editing by Anil D'Silva)