NUSA DUA, Indonesia—U.S. Treasury Secretary Janet Yellen said some sanctions on Russia could remain in place even after any eventual peace agreement with Ukraine, raising the prospect of a long-term U.S. effort to squeeze Russia’s economy.

As Ukraine makes advances on the battlefield, Western leaders have started to contemplate how and if an end to the war may be negotiated with Russia. Ukrainian President Volodymyr Zelensky recently said he was open to “genuine peace talks” with Russia, and U.S. officials have said that any settlement would be up to Ukrainians.

Ms. Yellen said any eventual peace agreement would involve a review of the penalties the U.S. and its allies have imposed on Russia’s economy.

“There really hasn’t been any effort on Russia’s part to want to undertake negotiations with Ukraine on any terms that are acceptable to Ukraine,” Ms. Yellen said in an interview in Indonesia, where she is attending a gathering of G-20 leaders. “I suppose in the context of some peace agreement, adjustment of sanctions is possible and could be appropriate.”

“We would probably feel, given what’s happened, that probably some sanctions should stay in place,” she said.

The U.S. and its allies have sought to degrade Russia’s military capabilities by cutting its access to advanced Western technology and squeezing its financial system. Still, Russia has made huge revenues on its energy sales this year, and Ms. Yellen has led an effort for the Group of Seven advanced nations to impose a price cap on Russia’s oil in response.

The price cap would bar firms in the G-7 and Australia from providing maritime services like insurance to shipments of Russian oil unless the oil is sold below the cap. The goal is to simultaneously reduce Russia’s revenue from its oil sales, while still keeping it available on global markets to stabilize prices.

The effort has faced delays as officials work to finalize its details—including the dollar amount for the cap—before it goes into place for Russian crude on Dec. 5. A sticking point has been how the European Union has planned to enforce the price cap, according to people familiar with the matter.

When it gave preliminary approval to the price cap plan in October, the EU expanded the planned measure to apply it directly to shipping, along with secondary services like insurance and financing. Under those EU rules, ships that carried Russian oil above the price cap would lose access to European maritime services for any future oil shipments, Russian or otherwise.

Those penalties worried U.S. officials, according to people familiar with the matter. They were concerned that ships based in Europe and other jurisdictions would avoid carrying Russian oil at all if it meant they could risk losing access to European insurance and financing for future, non-Russian oil shipments, the people said. U.S. officials have sought to make enforcement of the price cap relatively light to entice firms to ship Russian oil under it, which they view as a necessary step to protect the global economy from a major oil price surge this winter.

““It’s hard to know what Russia’s response is going to be. I don’t think that they can really afford to shut a lot of oil in. They need the revenue.””

— U.S. Treasury Secretary Janet Yellen

In the interview, Ms. Yellen said she has worked with her European counterparts to ease the shipping provision. “We spent some time discussing this with them and discussing their implementation. And I think we’re in a reasonable place on it,” she said.

The push is the latest U.S. effort to pull back European sanctions on Russia that they worry could have dire consequences for the global economy. The Biden administration hatched the price-cap plan itself as a way to relax Europe’s total ban on financing and insuring Russian oil as they worried about the possibility of large quantities of Russian oil coming off global markets.

A central question hanging over the price cap is whether Russia will cut off its oil exports to retaliate against a Western effort to dictate the price of its most important commodity. Russian officials have said they won’t sell oil under the price cap.

“It’s hard to know what Russia’s response is going to be. I don’t think that they can really afford to shut a lot of oil in. They need the revenue,” Ms. Yellen said.

Ms. Yellen and other Biden administration officials have said that the price cap may still ultimately reduce Russia’s revenue even if it refuses to sell under the cap. Maritime insurance and trade financing is limited outside of the major G-7 economies, meaning Russia would have to rely on more expensive and less established services to sell its oil. They also believe buyers may still demand a price near the Western cap even if they are dealing outside of it.

Ms. Yellen said that the U.S. could take steps like drawing oil from the Strategic Petroleum Reserve if Russia does intentionally cut off its oil exports.

“We think the price cap is gonna work and we still have possibilities with the Strategic Petroleum Reserves that we could use,” she said.

Write to Andrew Duehren at andrew.duehren@wsj.com