Traffic once again seized up in the Strait of Hormuz as both Tehran and Washington imposed separate blockades, with Iranian vessels continuing to test the US shutdown, tracking data showed on Monday.
Iran announced on Friday that it would reopen the strategic waterway, but the United States did not reciprocate for vessels going to and from Iranian ports.
Dozens of commercial vessels passed through the strait before Iran reclosed the passage on Saturday, later warning that any approaching ship would be treated as a target.
Since Sunday, only four ships have made the crossing in either direction, according to marine tracking firm Kpler.
One of those, the Iranian-flagged Nova Crest that is sanctioned by the US, headed out of the Gulf at around 0400 GMT on Monday, and continued to make its way through the Gulf of Oman, according to Marine Traffic.
However, it is usually when a vessel reaches the Iranian border with Pakistan that the US imposes its blockade.
Iran allowed the sanctioned gas tanker Axon I to enter the Gulf on Monday, destined for the UAE and therefore not subject to the US blockade.
Gas tanker G Summer crossed in the opposite direction on Sunday, having gone into the Gulf earlier in the week, but did not appear to dock at an Iranian port.
It was last detected close to the open sea near the Omani capital of Muscat.
The fourth vessel to cross was the Panama-flagged Starway, owned by China-based firm Hechuang International Group, according to Bloomberg.
The tanker passed westwards through the Iran-approved route at around 0800 GMT on Monday, but made a U-turn around 1200 GMT and was last detected heading back towards the strait.
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