A passenger train derailed in eastern India on Wednesday, killing four people after a suspected explosion on the tracks, officials said.
Some 12 carriages of the Delhi-Dibrugarh Rajdhani Express, which was travelling from the capital New Delhi to the northeastern state of Assam, toppled over at around 2:00 am (2030 GMT) in Bihar state's Saran district.
"Prima facie, it appears to be a case of sabotage," Railway Board chairman Arunendra Kumar told the Press Trust of India (PTI) news agency. "There was a blast on the track, which could have caused the derailment."
Maoist rebels had earlier called for a strike in the area to protest against the security forces.
Railway Minister Sadananda Gowda said there was no confirmation about what caused the derailment.
"As far as the Rajdhani Express is concerned we practically don't have much news about the cause of derailment (but) of course there was a bandh (shutdown) call given by Maoists," he told reporters.
A senior police officer, Superintendent Sudhir Kumar, said that a thorough investigation had been ordered into the incident, adding that a "technical fault" could also have been the cause.
If confirmed as an attack by the Maoists, it would be the first by the insurgents since Prime Minister Narendra Modi's right-wing Bharatiya Janata Party came to power last month after an election victory over the ruling Congress.
Separatist insurgencies affect large swathes of India's northeast, northwest and central regions, including the states of Chhattisgarh, Orissa, Bihar, Jharkhand and Maharashtra.
Many of the rebels say they are fighting authorities for land, jobs and other rights for poor tribal groups.
The Maoist insurgency has cost thousands of lives.
Eight other passengers were taken to hospital for treatment for their injuries following Wednesday's derailment.
One of the casualties, Ram Pratap Singh, described how passengers in sleeper carriages had been woken by a "loud noise".
"The carriage tipped over and over again and a passenger on a top (berth) fell on me," Singh told the ABP network.
"Then we got up somehow and found a small opening to get out," he told the channel.
Stranded passengers were being ferried in special trains while railway workers were trying to fix the long stretch of broken tracks.
It is the latest deadly incident on India's dilapidated rail network, which is still the main form of long-distance travel for the middle-class and the poor.
Last month, 26 people were killed when a passenger express travelling in the northern state of Uttar Pradesh ploughed into a stationary freight train.
In 2012, a government report said almost 15,000 people were killed every year on the network, describing the deaths as an annual "massacre" due mainly to poor safety standards.
Modi's government has pledged to revive the railway network by infusing funds and introducing new, modern trains.