Two cargo ships have reportedly come under fire in the Strait of Hormuz, the British maritime agency has said.
UK Maritime Trade Operations (UKMTO) said the first vessel was "attacked by an Iranian Revolutionary Guard Corps (IRGC) gunboat".
Nour News, a website affiliated with Iran's Supreme National Security Council, said the IRGC opened fire after the ship had "ignored the warnings of the Iranian armed forces".
A second ship was stopped in the strait after being "fired upon", UKMTO said, without saying who was responsible. Crews from both ships are safe, the agency said.
The reports come hours after US President Donald Trump announced an extension to the ceasefire with Iran until talks come to a conclusion.
The initial two-week truce between the US and Iran was due to expire on Wednesday, but Trump said he had been asked to hold off on attacking Iran by Pakistan, which has been acting as a mediator.
Trump, who said the US blockade of Iran's ports would continue, also said the Islamic republic was "collapsing financially" due to the blockade of Hormuz.
Although Iran is yet to comment on Trump's announcement, its foreign ministry earlier told the BBC that Tehran had still not decided whether it will attend a new round of peace talks with the US.
BBC Verify understands that the first ship targeted by the IRGC on Wednesday morning is called the Epaminondas.
The vessel is owned by a Greek company and, according to AIS data from Marine Traffic, was not transmitting a detectable signal while crossing the strait.
Reports from both UKMTO and Vanguard indicate that the ship's master had been told the vessel had permission to transit the strait.
However, it was approached by an IRGC gunboat, which opened fire and caused significant damage to the bridge.
BBC Verify also understands the second cargo ship targeted in the strait is the Panama-flagged Euphoria. It is owned by a UAE-based company and data shows that Jeddah in Saudi Arabia is listed as its destination.
It is not clear who targeted the second vessel. In a statement, UKMTO said it "is aware of high levels of activity in the SoH [Strait of Hormuz] area and encourages vessels to report any suspicious activity".
The ceasefire has brought some respite to the Middle East region, which had been engulfed for weeks in war since the US and Israel attacked Iran on 28 February.
On 8 April, Iran and the US agreed to a conditional two-week ceasefire, which was due to expire on Wednesday.
Initially, Trump said the deal was agreed on the condition that Iran reopens the Strait of Hormuz, a vital shipping route for oil and other exports from the Gulf.
Iran agreed to allow vessels through the strait for two weeks, with their passage coordinated by the Iranian military.
With no concrete agreement yet in place, uncertainty has remained and brought little relief to global markets.