A train accident in southwestern Germany that killed at least three people Sunday was likely caused by a landslide triggered by heavy rain, police said Monday.

"The water triggered a landslide in the embankment area near the tracks, which in turn probably caused the derailment," investigators said.

Three people were killed when a regional train carrying some 100 people derailed near Riedlingen, some 160 kilometres west of Munich, on Sunday evening.

Police forensic experts were set to examine the crash site Monday morning to determine exactly how the accident unfolded, a spokesman said.

It was initially unclear whether the train's tachograph had already been recovered from the vehicle.