International crude oil prices were near 2019 highs on Tuesday after Washington announced all Iran sanction waivers would end by May, pressuring importers to stop buying from Tehran.
Brent crude futures were at $74.40 per barrel at 0239 GMT (8:09 am in India), up 0.5 per cent from their last close and not far off a 2019 peak of $74.52 reached on Monday.
US West Texas Intermediate (WTI) crude futures hit their highest level since October 2018 at $65.95 per barrel before edging back to $65.89 by 0239 GMT, which was still up 0.5 per cent from their last settlement.
The United States on Monday demanded that buyers of Iranian oil stop purchases by May 1 or face sanctions, ending six months of waivers which allowed Iran's eight biggest buyers, most of them in Asia, to continue importing limited volumes.
Before the reimposition of sanctions last year, Iran was the fourth-largest producer among the Organization of the Petroleum Exporting Countries (OPEC) at almost 3 million barrels per day (bpd), but April exports have shrunk well below 1 million bpd, according to ship tracking and analyst data in Refinitiv.
Barclay's bank said in a note following the announcement that the decision took many market participants by surprise and that the move would "lead to a significant tightening of oil markets".
The British bank added that Washington's target to cut Iran oil exports to zero posed a "material upside risk to our current $70 per barrel average price forecast for Brent this year, compared with the year-to-date average of $65 per barrel".
ANZ bank said in a note on Tuesday that "the decision is likely to worsen the ongoing supply woes being felt with Venezuelan sanctions, the OPEC supply cut, and intensifying conflict in Libya".
The move to tighten Iran sanctions comes amid other sanctions Washington has placed on Venezuela's oil exports and also as producer club OPEC has led supply cuts since the start of the year aimed at tightening global oil markets and propping up crude prices.
Ellen Wald, non-resident senior fellow at the Global Energy Center of the Atlantic Council, said the United States "seem to expect" Saudi Arabia and the United Arab Emirates to replace the Iranian oil, but she added "that this is not necessarily the way Saudi Arabia sees it".
Saudi Arabia is the world's biggest exporter of crude oil and OPEC's de-facto leader. The group is set to meet in June to discuss its output policy.
"Should OPEC decide to end their supply cut programme going into the second half of the year, this could limit oil's upside in the coming months," said Lukman Otunuga, analyst at futures brokerage FXTM.
Meanwhile, the Atlantic Council said the US move would hurt Iranian citizens.
"We're going to see their currency collapse more, more unemployment, more inflation," said Barbara Slavin, director for the Future of Iran Initiative at the Atlantic Council, adding that the US sanctions were "not going to bring Iran back to the (nuclear) negotiating table".