Just two tankers transited the key energy chokepoint of the Strait of Hormuz on Monday, for the lowest daily tally of commodity vessels since early May, with both entering the Gulf, shipping data showed.
The figure was also well below the 10-day average of 14, with one very large gas carrier and one very large crude carrier entering the strait from the Gulf of Oman, according to shiptracker Kpler by 0657 GMT on Tuesday.
While down from Sunday's tally of seven vessels of all types, the figures could change, as some ships had switched off navigation transponders on their way through.
Separate provisional data from shiptracker Vortexa showed that Monday oil transits at 5 million barrels per day. On a seven-day moving average, Hormuz transits stand at around 6 million to 7 million bpd by August 23.
Iran said it had blacklisted 45 tankers for violating its rules on passage through the strait, threatening action against vessels engaging in ship-to-ship transfers with them, escalating pressure over the key waterway six months into the Iran war.
"It remains to be seen how Iran's Persian Gulf Strait Authority can enforce compliance by such 'non-compliant' vessels," said Xavier Tang, a senior market analyst at Vortexa.
"If conflict in the region escalates or vessels are attacked at the chokepoint, Hormuz transit could be affected."
Before the conflict, the strait carried about a fifth of global flows of crude oil and liquefied natural gas.
Iran also vowed to retaliate against expanded U.S. sanctions aimed at cutting off its economic lifeline, while expressing confidence that its major trading partners would resist Washington’s pressure campaign.
U.S. Treasury Secretary Scott Bessent unveiled the measures on Monday but stopped short of imposing the most severe sanctions. Countries continuing to trade with Iran risked losing access to the dollar-based financial system, he warned.
On Monday, 30 vessels transited Bab el-Mandeb, another key chokepoint on the opposite side of the Arabian peninsula, Kpler data showed. That was broadly in line with the 10-day average and compared with 28 crossings on Sunday.
(Reuters - Reporting by Siyi Liu in Singapore; Editing by Christian Schmollinger and Clarence Fernandez)