Singapore shares closed in the red zone on Tuesday, despite broader regional gains as US President, Donald Trump, warned Iran of its "complete demolition" ahead of the deadline to fully reopen the Strait of Hormuz.

The Straits Times Index (STI), a key benchmark for the Singapore Exchange, ranged between 4,947.33 and 4,990.59 throughout the day. It ended the session at 4,958.01, down 14.39 points or 0.3% compared to Monday's close.

In economic news, Singapore's foreign exchange reserves rose to SG$540.9 billion in March from SG$526.2 billion in February, according to data from the Monetary Authority of Singapore.

On the corporate front, shares of Top Glove (SGX:BVA, KLSE:TOPGLOV) were up over 2% at the close as it issued 500 new ordinary shares worth SG$0.40 apiece, arising from the exercise of warrants.

Nam Cheong (SGX:1MZ) was up over 1% as it secured offshore support vessel (OSV) charters worth up to 102.5 million ringgit for two vessels in Sarawak, Malaysia.

Meanwhile, Singapore Telecommunications (SGX:Z74) shares closed over 1% lower as it disclosed a plan to transfer special discounted shares (SDS) from the Central Provident Fund (CPF) Board to the Central Depository (CDP) accounts of SDS holders.