Front-month Brent crude futures LCOc1 were at $72.41 per barrel at 0348 GMT on Monday, down 42 cents, or 0.6 percent from their last close, according to Reuters.
US West Texas Intermediate (WTI) crude futures CLc1 were down 35 cents, or 0.6 percent, at $62.79 a barrel.
Both Brent and WTI have lost more than 15 percent in value since early October, in part as hedge funds have cut their bullish wagers on crude to a one-year low, data showed on Friday.
Washington re-introduced sanctions against Tehran on Monday, restoring measures lifted under a 2015 nuclear deal negotiated by the administration of President Barack Obama, and adding 300 new designations including Iran’s oil, shipping, insurance and banking sectors.
Despite this, oil prices came under pressure as Washington will allow several countries to continue importing crude from Iran despite the sanctions.
“The impact of the sanctions is going to be largely softened as a result of this allowance,” said Sukrit Vijayakar, director of Indian energy consultancy Trifecta.
The United States said on Friday it will temporarily allow eight importers to keep buying Iranian oil.
Washington has so far not named the eight, referred to as “jurisdictions”, a term that might include Taiwan which the United States does not regard as a country.
China, India, South Korea, Turkey, Italy, the United Arab Emirates and Japan have been the top importers of Iran’s oil, while Taiwan occasionally buys Iranian crude.
South Korea said on Monday it has been granted a waiver to at least temporarily continue to import condensate, a super-light form of crude oil, from Iran and also still continue financial transactions with the Middle East country.
Japan said on Monday it was in close communication with the United States. While Chief Cabinet Secretary Yoshihide Suga declined to detail any potential sanction waivers, he said his government had asked Washington that sanctions should not have an adverse impact on Japanese companies.