The threat to ships carrying oil in the Middle East is at its worst since the Iran war started, experts have said, after a spate of attacks on another key route in the region.
The warning comes after a number of attacks on vessels in the Red Sea, an alternative waterway that some tankers had been using since Iran blocked the Strait of Hormuz.
Iran has denied Donald Trump's claim that it was in talks with the US over reopening the strait, but said it was speaking to Oman about securing the shipping lane.
"In terms of threat to the trade of crude, we're at the worst period that we've been in since this since this crisis began," said Matthew Wright, an analyst at ship-tracking firm Kpler.
The number of ships passing through the Strait of Hormuz was just eight on Sunday and 11 on Saturday, compared with more than 100 per day before the war began, according to Kpler.
Before the conflict, about 20% of the world's oil and gas passed through the strait.
The temporary peace deal with the US struck in early June led to numbers rising again, but the resumption of strikes between the two countries roughly a month later have significantly reduced traffic.
Many ships have been "going dark" when crossing the strait, meaning they turn off their transponder to avoid detection.
For much of the war, some ships carrying oil from Saudi Arabia had instead passed through an alternative shipping lane in the Red Sea, between the kingdom and west Africa.
But a recent spate of attacks by Yemen's Houthi fighters on Saudi tankers using the alternative waterway has further heightened the risks.
The Iranian-backed Houthi militia announced what it called a blockade on Saudi Arabia's Red Sea ports on 20 July and the UK Maritime Trade Operations agency has reported several attacks on ships in the past week.
"Not only is the ongoing situation in the Strait of Hormuz constraining oil flows, but now a big factor that was helping to balance the market is now also under threat. It's a problem stacked on top of a problem," Wright said.
Tim Wilkins, the managing director of Intertanko, a trade body representing tanker owners, said the industry was "facing a broadening, deteriorating, and increasingly complex security situation".
"We now have the high-risk area going up to Saudi Arabian waters and extending into parts of the Red Sea. So that's having another impact on the market, on freedom of navigation as well."
The number of commodity vessels that passed through the Bab el-Mandeb strait was 28 on Saturday and six of them had their transponders turned off, according to Kpler data, indicating that they were trying to avoid detection.
Not all vessels are deterred from passing through because the Houthi threat is only targeted at Saudi shipping, with the total number sitting at about 50% of pre-attack levels.
But the number of ships loading crude oil for export to Asia passing through has dropped to about four per day, Kpler added, the lowest point since the start of the war.
A spokesperson for Hapag-Lloyd, the global shipping giant, said some of its vessels were still passing through the Red Sea but that it would "monitor developments closely and will adjust the network if circumstances change".
"If the Strait of Hormuz reopened, most ships could probably leave the region fairly quickly. However, restoring normal cargo flows would take much longer.
"Services have been suspended and ships redeployed elsewhere, so a return to normal flows would most likely take three to four months."
Despite the talks with Oman, Iran has said that no deal is imminent that would reopen the strait to normal traffic.
Its foreign ministry ministry spokesman Esmaeil Baqaei said any agreement would not lift the current restrictions while US "aggression" continued.
Kpler's Wright said that while talks with Oman could be productive, any deal would need the involvement of the US and the fear is that current negotiations could be a "false start" without concessions on at least one side.
Nonetheless, oil prices fell sharply after Trump said he would cancel planned strikes on Iran based on the potential for upcoming talks.
Brent crude was trading 4.4% lower at $84.05 a barrel, after it fell as much as 7.3% to $81.55 a barrel earlier in the day.
Peter Sand, chief analyst at Xeneta, another ship-tracking company, said the fighting had taken the shipping industry "back to to square one" and that things were in "a terrible state, regardless of which shipping type you're you're looking at".
"The alternatives for getting cargo, whether that's hydrocarbons or container shipping, are really not great… it is really still troubling times with no clarity and no change of fortunes within sight."
