Singapore shares started the week in negative territory as global oil prices climbed amid renewed tensions between the US and Iran in the Middle East.
The Straits Times Index (STI) opened 9.51 points, or 0.16%, lower on Monday at 5,792.450.
Global crude prices surged after the US military said it struck three Iranian oil tankers after US Navy warships were attacked.
Tehran has laid out plans for an "exclusion zone" outside the Strait of Hormuz, which will target vessels it believes are attempting to transit the contentious waterway.