Singapore is reporting an increase in sightings of “shadow fleet” tankers carrying sanctioned cargo off its shores. These vessels often conceal their identities, change flags and switch off tracking systems. Most are old and poorly maintained, increasing the risk of accidents and environmental disasters. Experts say they pose serious safety concerns in one of the world’s busiest shipping lanes.

Al Jazeera’s Patrick Fok reports from Singapore. Jennifer Parker is a specialist in maritime law and security at the University of New South Wales and a former naval officer. She said shadow fleets are hard to track because they operate outside normal rules.