India's railway authorities are continuing to try to identify the cause of a deadly train crash that occurred in the eastern state of Odisha one month ago.

An express train traveling to the southern city of Chennai entered a loop line, collided with a stationary freight train and derailed on June 2.

Some of the derailed carriages then hit another express train.

The multiple-train crash left more than 290 people dead and more than 1,000 injured.

The tracks have been restored, and service has resumed.

The authorities have indicated that a change made to the system that switches signals and tracks caused the accident, but details have not been revealed.

Indian media say the board investigating the accident has compiled the results of the probe, but the content has not been disclosed.

Investigators are reportedly considering charges of negligence resulting in death, and others.

Railway Minister Ashwini Vaishnaw told local media that it is necessary to know the actual facts and the technical root cause. He added that future steps will be decided after the investigation is completed.