Oil prices rose on Tuesday to their highest level in 4 weeks, as the United States reimposed a naval blockade on Iran and the two countries escalated attacks in the Strait of Hormuz, increasing uncertainty about energy flows.

Brent crude futures stood at $85.20 a barrel at 06:30 GMT, up $1.90, or 2.3%, while U.S. West Texas Intermediate crude rose to $80.05 a barrel, up $1.91, or 2.4%.

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Both contracts had earlier risen by more than $2 before paring some gains, while Brent crude posted a 9.6% gain in the previous session, its biggest daily increase since May 2020. The U.S. military carried out a third consecutive night of strikes on Iran on Monday, as U.S. President Donald Trump reimposed a blockade on Iranian navigation and proposed a 20% tariff to protect the Strait of Hormuz. Shipping data on Monday showed the number of oil tankers transiting the Strait of Hormuz over the past day fell to its lowest in two months.

"The recent escalation, including the U.S. reimposition of the blockade and Iranian responses, has clearly increased risks in the market," said Tim Waterer, senior market analyst at KCM Trade.

"Although there has been no complete closure of the strait, the conflicting objectives of the two sides have made the supply situation highly unstable," he added.