US crude oil prices have pushed above $70 a barrel for the first time in over three years as concerns have grown over supplies from Iran and Venezuela. West Texas Intermediate, the US oil benchmark, reached $70.84 on Monday, up 1.6 percent for the session and the highest level since November 2014. The North Sea’s Brent grade also reached a three-and-a-half year high of more than $76. Robust demand propelled by solid economic growth, along with cuts in output co-ordinated by the Opec cartel, have diminished surplus oil stocks and left the market more sensitive to shocks.

Concerns over supplies have centered on Iran, which faces the return of US sanctions, and Venezuela as economic turmoil dents its crude sales. Iran’s oil production has bounced back to nearly 4m barrels a day since world powers eased sanctions over its nuclear programme. President Donald Trump has threatened to reimpose the sanctions, which could reduce Iranian oil exports by 200,000-300,000 barrels a day, according to RBC Capital Markets.

The White House must decide by Saturday whether to extend waivers on the sanctions. Mr. Trump tweeted on Monday that he would announce his decision at 2 pm eastern time on Tuesday. Venezuela’s oil production has fallen by nearly 600,000 barrels a day from a year ago due to “chronic mismanagement” inside the country, the International Energy Agency said, helping Opec easily meet compliance targets. In a further blow, ConocoPhillips, the US exploration and production company, won court rulings at the end of last week giving it control of assets owned by Venezuelan state oil company PDVSA, raising questions about fresh disruptions to the country’s exports.