RAIL transport operator SMRT and regulator Land Transport Authority (LTA) said they are working with a team of experts from French train manufacturer Alstom on the recent spate of signalling problems experienced on the Circle Line.
The issue has caused slower trains and longer waiting times this week.
"To date, we have narrowed the problem to signal interference, causing intermittent loss of signal between trains and stations," SMRT and LTA said in a joint statement on Thursday morning.
"We are working round the clock to restore service levels. However, as the Circle Line runs underground, trackside checks and physical interventions can only take place after operating hours although backend system checks are being conducted throughout daylight hours."
Commuters along the Circle Line may experience delays and should factor in extra travel time, the statement said.
"SMRT's Operations Control Centre is being manned closely and additional staffing have been deployed on board trains for expeditious service recovery. More staff will also be deployed at stations to re-direct passengers, in the event that additional assistance is needed by those seeking alternative travel options."
SMRT shares last traded at S$1.645.