Oil tankers and cargo ships sat at anchor off Port Sultan Qaboos in Muscat, Oman, on June 21, 2026. The Strait of Hormuz, one of the world’s most critical corridors for oil and gas shipments, has been effectively blockaded since war broke out between the United States and Iran in late February. On Sunday, U.S. Vice President JD Vance arrived in Switzerland for senior-level negotiations with Iranian officials, as both sides work to define the terms for ending the conflict.
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Vessel movement through the Strait of Hormuz slowed sharply over the weekend, maritime intelligence firm Windward reported, after Iran said it had once again closed the world’s most important oil chokepoint.
The disruption came despite tracking data showing that Iranian tankers were still moving through the narrow waterway, which normally carries about 20% of global oil traffic.
Tanker activity had briefly picked up after the U.S. and Iran signed a 14-point memorandum of understanding last week, raising hopes that shipping conditions might begin to normalize. The latest figures, however, suggest that recovery has already faltered.
Windward’s analysis showed that only 12 ships passed through the Strait of Hormuz on Sunday, down from more than 21 a day earlier. Of the eight vessels entering the strait, five were reportedly “dark,” meaning they had turned off their Automatic Identification System, or AIS, transponders to conceal their location, identity and destination.
“The current traffic profile: dark, sanctioned, Iranian-linked, resembling the late-blockade baseline more than a functioning open strait,” Windward said Sunday in a post on social media.
Trade intelligence company Kpler said last week that at least 20 tankers crossed the Strait of Hormuz on Thursday, the highest level of traffic recorded since June 2. Even so, that remained well below prewar norms, when more than 100 vessels moved through the strait each day, including dozens of tankers.
A separate analysis published Monday from maritime specialists Lloyd’s List also found that commercial traffic continued to move through the Strait of Hormuz over the weekend, defying Iran’s claims that it had closed the waterway once again.
Iran on Saturday said that it had shut the strategically vital strait, citing ceasefire violations after Israel continued deadly strikes in southern Lebanon.
The U.S. military denied those claims, stating that the waterway remained open and that “Iran does not control the Strait of Hormuz.”
At least 15 Iran-flagged Suezmaxes and very large crude carriers, or VLCCs, were outbound from the Gulf of Oman with AIS signals active as of Saturday night, according to Lloyd’s List.
U.S.-Iran talks in Switzerland
The U.S. and Iran held talks in a Swiss mountain resort on Sunday to build on the memorandum of understanding both parties signed on Wednesday.
Both parties were said to have made progress on reaching a final deal within 60 days during the talks, including the agreement to establish a committee and a mechanism to end hostilities in Lebanon.
A senior Pakistani official and an Iranian official, who were involved in the talks in Bürgenstock, have told MS NOW the talks went into the early hours and were “constructive but tense.”
Under the MOU, both sides agreed to reopen the Strait of Hormuz toll-free for at least 60 days and to end all hostilities, including in Lebanon, where fighting has persisted between Israel and Iran-backed Hezbollah.
Iran’s foreign minister, Abbas Araghchi, said the country had secured waivers for oil and petrochemical exports, the lifting of the blockade on its ports, the release of some frozen assets, and the launch of a reconstruction and development plan.
President Donald Trump had threatened further attacks on Iran ahead of the talks in Switzerland. “Iran must immediately stop their highly paid PROXIES in Lebanon from causing trouble. If they don’t, we’ll hit Iran very hard again, just like we did last week, only harder!!!” Trump said in a social media post on Sunday.
Large commercial vessels and a small boat navigate the waters off the southern port city of Bandar Abbas, Iran on June 21, 2026.
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Vice President JD Vance, who led the U.S. delegation at the talks, said he was optimistic about the outcome of the Swiss talks despite Iran’s latest threat to shut the strait.
He also downplayed the impact of violence in Lebanon, saying progress had been made toward ending hostilities there. “These things are always a little bit messy,” Vance said.
— CNBC’s Anniek Bao and Spencer Kimball contributed to this report.
