RENO, Nev. — President Barack Obama announced today that the Justice Department is assembling a team to “root out any cases of fraud or manipulation” in oil markets that might be contributing to $4 a gallon-plus gasoline prices.

“We are going to make sure that no one is taking advantage of the American people for their own short-term gain,” Obama said at a town-hall style meeting at a renewable energy plant in Reno.

The national average price for a gallon of regular gasoline was $3.84 today, about 30 cents higher than a month ago and almost a dollar higher than a year ago.

Obama, decrying such levels as yet another hardship “at a time when things were already pretty tough,” said Attorney General Eric Holder was forming the Financial Fraud Enforcement Working Group.

It will focus some of its investigation on “the role of traders and speculators,” Obama said.