Transport authorities suspect sabotage is to blame for the derailment of a northern train in Lamphun province on Saturday evening.
Deputy Transport Minister Chatt Kuldiloke yesterday said the derailment of the Chiang Mai-Bangkok train in a forest near Ban Nong Lom village of Muang Lamphun district was probably the result of an internal conflict in the State Railway of Thailand (SRT).
He suggested the incident was an "act of sabotage" intended to discredit some SRT executives.
Other derailments have occurred recently, and the deputy minister has ordered the SRT to investigate.
SRT governor Yutthana Thapcharoen yesterday denied a report that the driver or the engineer of the Chiang Mai-Bangkok train had been drunk and had caused the derailment.
He said the accident was due either to the condition of the railway tracks, or a sabotage attempt that may involve outsiders.
"Checks of the site found many causes for suspicion," Mr Yutthana said.
"For example, tracks there were found lying as far as 8-10 metres away from where they should have been. Fish plates, and nuts and bolts were also missing.
"Normally only technicians with special tools can remove them. Civil engineers must be questioned."
The SRT governor said civil engineers had checked the condition of the northern tracks regularly over the past two weeks.
Mr Yutthana did not think the heat caused the derailment and said the SRT would conclude its investigation within a week.
Prakit Arasad, the derailed train's engineer, and driver Somkiat Kitsophi strenuously denied that they were drunk on duty.
Mr Prakit said bottles of beer were spotted at the site of the accident, but that meant nothing as beer was available for sale on all trains.
SRT staff removed the derailed train early yesterday and northern train services were able to resume operations later in the day.