Prices rose 4.2% for the year ending in May as inflation hit a three-year high, the government said Wednesday in a report that underscored the impact of war-related shocks to energy costs.

The Consumer Price Index rose 0.5% for the month, which was largely in line with Wall Street expectations. But it was the third straight monthly increase in the midterm election year.

The annual reading from the Bureau of Labor Statistics exceeded the 3.8% reading in April and was the highest yearly inflation number since April 2023.

Energy costs stood out as the main driver of inflation, accounting for more than 60% of the monthly all-items increase, according to the BLS.

Shelter and food costs rose slightly.

“Indexes that increased over the month include communication, airline fares, medical care, personal care, and recreation,” the report said. “Conversely, the indexes for motor vehicle insurance, household furnishings and operations, and new vehicles were among the major indexes that decreased in May.”

Rising costs and concerns about affordability have dominated the political conversation since the COVID-19 pandemic.

Rampant inflation dogged President Joseph R. Biden during his term, peaking at 9.1%. Mr. Trump campaigned on a promise to fix the problem. He saw early success in reducing the price of eggs and other goods.

However, his tariff policies complicated the picture, and his military operation against Iran led to energy shocks because Tehran retaliated by restricting commercial shipments in the Strait of Hormuz.

Oil prices rose slightly on Wednesday as Mr. Trump threatened to punish Iran for dragging out peace talks, and both sides renewed military attacks. Stocks were also down because of the new turmoil in the Middle East.

The U.S. average price of a gallon of gas stood at $4.15 on Wednesday, down from $4.52 a month ago but up 39% from when the war started, according to the AAA motor club.