Gasoline prices in the United States hit their highest level in four years on Tuesday as negotiations over the Iran war appeared to show little signs of a resolution.

The price of an average gallon of gas stands at $4.17, marking an increase of $1.19 per gallon since the war began on Feb. 28, AAA data showed. That amounts to a 28% jump in about two months.

The U.S.-Israeli war on Iran set off one of the largest global oil shocks in history, spiking fuel costs. Gasoline prices reached a previous high on April 9, but a U.S.-Iran ceasefire announced a day earlier ultimately put downward pressure on prices.

Gas prices have moved upward in recent days as oil prices rose in response to an apparent impasse in negotiations over the war.

The Middle East conflict prompted Iranian closure of the Strait of Hormuz, a maritime trading route that facilitates the transport of about one-fifth of global oil supply.

The U.S. is a net exporter of petroleum, meaning the country produces more oil than it consumes. But since oil prices are set on a global market, U.S. prices move in response to swings in worldwide supply and demand.

U.S. oil futures hovered around $99 a barrel on Tuesday, which amounted to a more than 50% price leap from pre-war levels.

Crude oil is the main ingredient in auto fuel, accounting for more than half of the price paid at the pump, according to the federal U.S. Energy Information Administration.