BRUSSELS — The struggling economies of France and Italy are out of step with better-performing countries like Germany, raising the prospect of more trouble for the euro zone, the European Union’s top economics official warned Wednesday.

France and Italy are among the nations in the beleaguered bloc that need to accelerate the policy changes needed to improve their competitiveness and help the euro zone exit a lingering economic crisis, said Olli Rehn, the European commissioner for economic and monetary affairs.

The uneven performance of economies using the euro is one of the main reasons for the severity of a debt crisis in which some of the worst affected countries were able to borrow more than they could repay.

While the Union has made some strides in rebalancing its economies, “it will take some time yet to complete the unwinding of the imbalances that were able to grow unchecked in the decade up to the crisis, and which continue to take a toll on our economies,” Mr. Rehn said at a news conference.