Editor's note: This article was updated at 5:25 AM CST.
Oil topped $74 a barrel on April 22, the highest since November, with the United States set to announce a further clampdown on Iranian oil exports, tightening global supplies.
The U.S. is expected to say later on Monday that buyers of Iranian oil need to end imports soon or face sanctions, a source familiar with the situation said, confirming an earlier Washington Post report.
"This does bring a lot more uncertainty in terms of global supplies," said Olivier Jakob, analyst at Petromatrix. "It is a bullish surprise for the market."
Brent crude, the global benchmark, rose as much as 3.3% to $74.31 a barrel, the highest since Nov. 1. It was up $1.94 at $73.91 at 0847 GMT.
U.S. West Texas Intermediate crude climbed by as much as 2.9% to $65.87, the highest since Oct. 31, and was last up $1.51 at $65.51.
In November, the U.S. reimposed sanctions on exports of Iranian oil after President Donald Trump unilaterally pulled out of a 2015 nuclear accord between Iran and six world powers.
Washington, however, granted waivers to Iran's eight main buyers - China, India, Japan, South Korea, Taiwan, Turkey, Italy and Greece - that allowed them to continue making limited purchases for six months.
U.S. Secretary of State Mike Pompeo is due make an announcement on Monday, the Washington Post said.
Another drop in Iranian exports would further squeeze supply in a market already tightened through the U.S. sanctions against Iran and fellow OPEC member Venezuela, plus voluntary cuts led by OPEC.
An end to the exemptions would hit Asian buyers hardest. Iran's biggest oil customers are China and India, both of which have been lobbying for an extension to the sanction waivers.
The prospect of reduced Iranian supply brought a cautious reaction from top OPEC exporter Saudi Arabia, a key U.S. ally and also a driving force behind the OPEC-led supply-cut deal.
A source familiar with Saudi thinking told Reuters on Monday Saudi Arabia is willing to compensate for any potential loss of crude supply but the kingdom will assess the impact on the market before raising its output.
Analysts at JBC Energy in Vienna see a Saudi supply boost as likely.
"It is now almost certain that additional volumes from Saudi Arabia from May onwards will come back into the market," JBC said in a report.
Saudi Energy Minister Khalid al-Falih said on Sunday there was consensus among OPEC and allied oil producers to drive down crude inventories "gently" but his country would remain responsive to the needs of what he called a fragile market.
White House hard-liners won internal debate to cancel waivers for eight importers of Iranian crude.
Asian shippers and refiners have put ships heading to the Middle East on alert and are expecting a possible rise in marine insurance premiums after recent attacks on Saudi oil tankers and pipeline facilities, industry sources said on Tuesday.