Fault in tracks was the possible cause of derailment of all the coaches of the Delhi-Kamakhya North East Express in Bihar, sources said on Thursday citing a preliminary investigation report.

At least four people were killed and several injured in the accident in Bihar's Buxar district Wednesday night.

"It seems that derailment occurred due to fault in tracks," the report, signed by six railway officials, stated.

Highlighting the condition of passenger coaches, the report stated that all 22 coaches and the engine derailed -- two of them were fully capsized and two others turned turtle.

The probe report has estimated the cost of damage due to the accident at more than Rs 52 crore.

The loco pilot, Vipin Kumar Sinha, suffered minor injuries and his assistant sustained serious injuries in the accident.

The report also contained a statement from Sinha who said that the train passed Raghunathpur station, near which the accident occurred, at a speed of 128 km per hour, but soon after it crossed the station section, it suffered a severe jolt at the rear end with excessive vibration.

As a result of the excessive vibration and the severe jolt, the brake pipe pressure dropped suddenly and the train derailed at 9:52 pm, the preliminary report quoted the loco pilot as saying.

According to Sinha's statement, he took charge of the train from Deen Dayal Upadhyay station at 8:27 pm when everything was fine. He said that the train reached Buxar at 9:29 pm when the assistant loco pilot again did an inspection of the engine and found everything fine.

The report also quoted a gateman and a pointsman at the Raghunathpur station as saying that they saw sparks coming from near the wheels of the train.

"As per statement from the gateman of LC (Level Crossing) Gate no 59B, train no 12506 passed the gate and just after passing 8-10 coaches, he observed sparking and heard heavy noise,” the report stated.

The report stated a breath analyser test of the loco pilot and his assistant was negative.

At least four people died and several were injured when the train derailed near Raghunathpur in Bihar's Buxar district on Wednesday night.

An eight-year-old girl, identified as Akriti Bhandari, and her mother Usha Bhandari (37) who were travelling to Assam were among the four passengers who died in the derailment, the chief public relations officer (CPRO) of the East Central Railway said.

"The girl's father, who was also travelling with them, survived the accident. Narendra Kumar from Rajasthan and Abu Zayed (27) from Purnia were the other two who lost their lives. Zayed's friend, who was travelling with him, survived the accident,” the CPRO added.

He also informed that many people, who received minor injuries and were discharged within hours of the accident, were accommodated in a special train which left for the destination stations.

"Based on the medical advice of doctors, we are providing ambulance facilities to passengers to be dropped at home even if they are from distant places in Bihar and West Bengal,” the CPRO said.