NEW YORK (AP) — U.S. gas prices jumped to an average of $4 a gallon again Monday as the U.S. and Iran launched more attacks.

According to motor club federation AAA, the national average for a gallon of regular gasoline is now back to $4. The average price a year ago was $3.14 a gallon.

The price is a national average, meaning drivers in some states have been paying well over $4 a gallon for a while now, while others pay less. Prices vary between states due to factors ranging from nearby supply to differing tax rates.

People around the world are also dealing with high gas prices as a result of the war.

Gas prices first went over $4 a gallon on average at the end of March. They dipped below that in mid-June and continued to fall as crude oil prices eased when the U.S. and Iran reached an interim deal. Even then, President Donald Trump expressed frustration that gas prices weren’t falling as quickly as oil prices.

Affordability is likely to be a key issue for voters in the U.S. midterm elections, and higher gas and oil prices can help push up prices for groceries and other goods.

Oil prices have climbed again in recent days as the U.S. and Iran move closer to resuming an all-out war.

Brent crude, the international standard, fell slightly by Monday morning trading in the U.S. — down $1.64 to $86.46 per barrel. But that's still much higher than prewar levels, when crude was going for close to $70 a barrel. Meanwhile, benchmark U.S. crude dropped $1.87 to $79.91 per barrel.