US Treasury Secretary Janet Yellen on Sunday said Americans could experience a spike in petrol prices in the winter when the European Union significantly cuts back on buying Russian oil, adding that a proposed Western price cap on Russia's oil exports is being designed to keep prices in check.

"It's a risk, and it's a risk that we're working on the price cap to try to address," Yellen told CNN.

The possible price increase could come because the EU "will cease for the most part buying Russian oil" and impose a ban on services that allow Russia to ship oil by tanker, she said.

The price cap plan agreed to by G7 wealthy nations calls for participating countries to deny insurance, finance, brokering, navigation and other services to oil cargoes priced above a yet-to-be-determined price cap on crude and oil products.

Yellen said the price cap is aimed at lowering revenue Russia could use to wage war in Ukraine while maintaining Russian oil supplies to keep global prices down. (Reuters)