“We are now learning of serious irregularities at this facility that are deeply concerning and demand a thorough investigation,” Barr said.
Oil prices fell on Wednesday on disappointing economic data from China and a rise in U.S. crude inventories, erasing some of the sharp gains in the previous session after the U.S. said it would delay tariffs on some Chinese products, easing trade tensions.
Brent crude was down 46 cents, or 0.8%, at $60.84 a barrel at 0639 GMT, after rising 4.7% on Tuesday, the biggest percentage gain since December.
U.S. oil was down 62 cents, or 1.1%, at $56.48 a barrel, having risen 4% the previous session, the most in just over a month.
China reported a raft of unexpectedly weak data for July, including a surprise drop in industrial output growth to a more than 17-year low, underlining widening economic cracks as the trade war with the United States intensifies.
"Deteriorating China industrial output and consumer spending suggest the fundamental picture isn't great and the demand for energy may be under the pressure," said Margaret Yang, market analyst at CMC Markets.
Profit taking after Tuesday's sharp gains also weighed on crude prices on Wednesday, analysts said.
"The moves in oil were so outsized overnight, that some profit taking in Asia was logical," said Jeffrey Halley, senior market analyst, Asia Pacific at OANDA.