Attacks around the waterway have surged over the past 10 days, with Iran saying it is stepping up strikes in response to the US blockade of its ports and tougher sanctions introduced last month.
The Singapore-flagged GFS Pride, a small container vessel, sank while sailing through the strait, according to maritime security sources.
"GFS PRIDE sustained damage and a fire on board, and has since sunk. All 21 crew members were safely evacuated. No injuries have been reported," the Maritime and Port Authority of Singapore (MPA) said in a statement, adding the vessel had been sailing through the strait on Tuesday.
In a separate incident, the Antigua and Barbuda-flagged Cape Dao sank close to the strait, weeks after being struck by a projectile on September 23, data from UN shipping agency the International Maritime Organization showed.
One crew member was killed, the rest of the crew evacuated straight after the strike, maritime sources said.
Its UAE-based manager Peonies Shipmanagement FZE could not be immediately reached for comment.
The GFS Pride and Cape Dao are the second and third vessels to have sunk since the US-Iran war began on February 28, according to an analysis of IMO casualty data.
"MPA is deeply concerned about the continued attacks on commercial shipping in the Strait of Hormuz," the Singapore authority said.
"Such attacks are unprovoked, unjustifiable, and a breach of international law."
GFS Pride's United Arab Emirates-based manager, GFS Ship Management FZE, could not be immediately reached for comment.
"The latest incidents reinforce the continuing threat to commercial shipping transiting the Strait of Hormuz," maritime risk management company MARISKS said.
"The threat is not confined to tankers, with container vessels and bulk carriers also sustaining serious damage."
A sharp escalation in threats to commercial shipping in and around the Strait of Hormuz, through which about a fifth of global oil and liquefied natural gas trade passed before the war, has heightened concerns about security in the waterway.
Tehran has sought to tighten its grip on the waterway since US and Israeli strikes on Iran on February 28, restricting transit in an effort to gain leverage over Washington.
Iran is increasingly deploying new tactics against vessels transiting the strait as it seeks to keep oil prices elevated and influence US midterm elections, two senior Iranian officials told Reuters.
While Iran and the US have focused their attacks on tankers, cargo and container vessels have also been attacked, immobilised or sunk.
The Maltese-flagged container ship Safeen Prestige was hit by a projectile in March and later sank north of the Strait of Hormuz.
Iran's Revolutionary Guards attacked and seized the container ship MSC Francesca in April.
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