Ships in the Gulf have received a warning from Iran's navy that any vessels seeking to cross the Strait of Hormuz without permission "will be targeted and destroyed", the shipping brokerage firm SSY has confirmed to BBC Verify.

A two-week ceasefire was agreed on Tuesday evening on the condition that "safe passage" through the narrow waterway is guaranteed - but only a few vessels have since crossed.

The strait has become a focal point of the US-Israel war with Iran after Tehran effectively choked off one of the world's most important shipping lanes, carrying about a fifth of the world's oil and liquefied natural gas.

The disruption, over the past five weeks, has sent shock waves across the world economy, pushing up energy prices and exposing just how reliant international supply chains are on the strait, which is only about 33km (21 miles) wide at its narrowest point.

As well as energy, the Gulf is also vital for transporting chemicals needed to process products like microchips, pharmaceuticals and fertiliser.

While the price of oil has fallen on news of the ceasefire, shipping analysts are warning to expect only a trickle of crossings for now.

"Most shipping lines would want to get details and reassurances on what it actually takes to transit and those details are not available," Lars Jensen from Vespucci Maritime told the BBC.

By 14:00 BST on 8 April just three bulk carriers - NJ Earth, Daytona Beach and Hai Long 1 - had passed through the strait since the ceasefire was announced late on Tuesday night.

That's based on BBC Verify analysis of ship-tracking data from MarineTraffic.

That compares to 138 ships that passed through the strait each day, on average, before the conflict started on 28 February.

We do not know if the three vessels that crossed on Wednesday were the result of the ceasefire, or whether they had already planned to make the journey.

"It is still too soon to tell whether this reflects a broader ceasefire-driven reopening or a previously approved exception," says Ana Subasic from the shipping analyst company Kpler.

"Nothing has really changed yet," adds Jensen, arguing it will take time before crews are confident enough to cross safely.

That view is echoed by Richard Meade, editor-in-chief of Lloyd's List, who says it has been a "very dangerous" time for ship owners who still face a huge amount of uncertainty.

"We know Iran is essentially still in control of the strait, and the assumption is that ship owners will still need to seek permission from the IRGC [Islamic Revolutionary Guard Corps]… and how that's going to work is still not clear."

BBC Verify's analysis of the paths taken by the three ships shows them taking a northern route through the strait close to Iran's coastline and entering its territorial waters.

Prior to the conflict, vessels usually took a more southerly route through the middle of the waterway.

'Nearly 800 ships stuck'

If crossings do resume, Meade expects that stranded tankers that are fully loaded with cargo will be the first through.

"You've had nearly 800 ships stuck in there for several weeks. Most of them are now loaded with cargo, so the priority is going to be to get them out."

The duration of the ceasefire - set to last two weeks - also brings uncertainty for ships, says Niels Rasmussen, a shipping analyst from BIMCO.

"I doubt there will be a large influx of ships into the Gulf… because they do not want to risk being trapped after the two-week window closes."

Another uncertainty is the possibility of sea mines, says Thomas Kazakos, secretary general of the International Chamber of Shipping.

"We need to make sure that we have clear confirmation that the safety of navigation for the ships and the seafarers are being agreed," he told BBC Verify.

Toll payments

On top of these concerns, ships face the uncertainty of possibly having to make payments to Iran in order to secure safe passage - following reports that tolls may be a part of the ceasefire deal.

"The Iranian negotiation position seems to be that you need to pay a toll to go through the strait and shipping lines will also be hesitant in going down the path of paying that toll," says Jensen.

Some countries - including India, Malaysia and the Philippines - have negotiated safe passage for their vessels in recent weeks.

But paying a toll could present an added complexity for other countries and shipping companies as payment "might actually be in violation of some of the US sanctions on Iran which would have other repercussions on shipping lines," adds Jensen.

Sanctions work by criminalising payments to individuals, companies and organisations, explains James Turner, a shipping lawyer from Quadrant Chambers.

He told BBC Verify that a sanction violation occurs when payment is made to anyone on the list, so paying a toll to them would be a violation unless the US makes an exception.

Despite the lack of crossings so far, markets responded positively in the hours following the ceasefire.

Benchmark Brent crude fell by about 13% to $94.80 (£70.73) a barrel, while US-traded oil was more than 15% lower at $95.75.

However, Meade says expectations still need to be tempered.

"Oil prices responded because it is a positive directional move, but I don't think it in any way suggests that we're going to see that 20% of global energy flowing back through at normal levels any time soon." (BBC)

Update news