Singapore shares closed higher on Monday, despite mixed regional performances, with US President Donald Trump issuing Iran yet another ultimatum to reopen the Strait of Hormuz.

The Straits Times Index (STI), a key benchmark for the Singapore Exchange, ranged between 4,943.43 and 4,973.30 throughout the day. It ended the session at 4,972.40, up 24.90 points or 0.5% compared to Thursday's close.

The US president threatened to target Iran's civilian infrastructure if the waterway was not opened by Tuesday.

In economic news, Singapore's total retail sales rose 8.3% year on year in February, according to data released by the Department of Statistics Singapore.

Meanwhile, the S&P Global Singapore Purchasing Manager's Index posted above the 50.0 no-change mark for the 14th straight month in March, according to data released by S&P Global.

On the corporate front, shares of Oiltek International (SGX:HQU) surged nearly 21% at the close as its subsidiary, Oiltek Malaysia, signed a heads of agreement with Bioseaga Industries, to provide construction services for a sustainable aviation fuel production facility in Sabah, Malaysia.

Olam's (SGX:VC2) subsidiary, Olam Holdings, agreed with Wipro to dispose of its entire 100% stake in Mindsprint for an estimated gain of around $310.5 million.

Meanwhile, SinoCloud's (SGX:LYY) chairman, Andrew Wai Men Chan, stepped down from the role, effective April 9.