Shippers say they need more clarity on the terms of a US-Iran ceasefire before resuming transit through the Strait of Hormuz as Iran issued fresh warnings about any vessels attempting to sail through the waterway.
The six-week conflict had brought traffic through the strait - a choke point for about 20 per cent of global oil and liquefied natural gas (LNG) shipments - close to a standstill, pushing global energy prices sharply higher.
Iran said it would offer safe passage in co-ordination with its armed forces, although its coastguards warned on Wednesday that any ship attempting to sail without permissions would be "targeted and destroyed".
The first vessel had transited the Strait with Iran's permission following the ceasefire, state TV said on Wednesday.
The ship's identity was not immediately clear but MarineTraffic data showed two Greek-owned and one Chinese-owned bulk carriers passing through since early Wednesday.
Iran has previously agreed safe-passage arrangements with several countries, including India and Iraq.
Major shipping companies remained cautious.
Denmark's Maersk said the ceasefire may create transit opportunities for vessels but did not yet provide full maritime certainty.
German container carrier Hapag-Lloyd said it needed to see that the ceasefire holds before starting to take orders for selected markets.
Restoring flows to normal could take at least six to eight weeks, its CEO Rolf Habben Jansen told a call with customers.
Lars Barstad, CEO of oil tanker group Frontline, said the firm was still assessing what the ceasefire meant for shipping.
"I want to see the fine print," he told Reuters.
Bimco Chief Safety and Security Officer Jakob Larsen warned that vessels leaving the Gulf without prior co-ordination with US and Iranian authorities would face heightened risk.
Ship tracker Kpler indicated 187 laden tankers carrying 172 million barrels of crude oil and refined products were inside the Gulf as of Tuesday.
Shipping sources said interest in loading Gulf cargoes had picked up among Asian refiners, as well as trader Glencore and French oil major TotalEnergies, both of which declined to comment.
UK Prime Minister Keir Starmer said on Wednesday there was still a lot of work to do to reopen the Strait, speaking during a visit to Saudi Arabia.
"We now ... have a ceasefire but there's a lot of work to do, as you will appreciate, a lot of work to make sure that that ceasefire becomes permanent and brings about the peace that we all want to see," he told UK and Saudi personnel during the visit.
"But also a lot of work to do in relation to the Strait of Hormuz, which has an impact everywhere across the world."
The Wall Street Journal newspaper on Wednesday quoted a crew member of a ship as saying that a radio message had stated that authorisation from Iran's Sepah navy would have to be obtained for a passage.
Without authorisation, the ship would be threatened with being destroyed, he said.
The Sepah navy is the maritime arm of Iran's Islamic Revolutionary Guard Corps.
with DPA