"Our preliminary assessment points to a possible power-related equipment failure at substations or along the track, or the undercarriage of a potential defective train which we are investigating tonight. But we are not ruling out other possibilities." SMRT President and CEO Desmond Kuek said: "SMRT has mobilised all engineering and technical staff to comprehensively check the entire network and train fleet. SMRT and LTA engineers are working round the clock to conduct tests, and sections of the network are being isolated to pin point the fault. "While it is still early to conclude the cause of the fault, we are doing our utmost to recover the system with the view to resume full train services as soon as possible. We deeply apologise for the inconvenience caused to all our commuters." Transport Minister Lui Tuck Yew said in a Facebook post: "I am extremely concerned with today's incident. This is the first time that services on both the North-South and East-West Lines were affected at the same time.