SARDIHA, India (AFP) – Maoist rebels derailed a high-speed train packed with sleeping passengers into the path of a freight train in eastern India on Friday, killing at least 71 people, police said.

It was the latest in a series of deadly Maoist attacks that have put the government under intense pressure to consider deploying the military as it struggles to contain the growing left-wing insurgency.

Police warned the death toll would rise with dozens more bodies feared trapped in the mangled wreckage after 13 carriages of the Mumbai-bound express from Kolkata careened off the tracks in a remote area of West Bengal.

Railways Minister Mamata Banerjee said the train had been derailed by a "severe bomb blast", but officials said they were also looking at evidence that metal plates used to secure adjoining sections of track had been removed.

"It is a clear case of sabotage. The Maoists have done it," West Bengal police chief Bhupinder Singh told reporters at the crash site. He said Maoist leaflets had been found scattered by the tracks.

The Press Trust of India said it had received a call claiming responsibility by the Maoist-backed People's Committee against Police Atrocities (PCPA), although a PCPA spokesman later contacted the news agency to deny the group's involvement.

Police inspector general Surajit Kar Purakayastha, who was helping coordinate the rescue operation, said emergency teams had recovered 71 bodies.

"We're doing all we can, but I'm afraid there are still more bodies trapped in some of the carriages," he told AFP.

More than 200 people were reported injured, some of them in critical condition.

Four of the carriages that slammed into an oncoming goods train were badly crushed and flipped on their sides with body parts clearly visible amid the twisted metal.

Rescue workers with bolt cutters struggled to free anyone still alive inside.

One survivor, Vinayak Sadna, said he had been sleeping when his carriage lurched violently to one side and then flipped over, flinging passengers around the compartment.

"I ended up stuck between two seats with an iron bar crushing my hand," Sadna said. "I was trapped for three hours before I was pulled out. My wife is still missing."

Another distraught passenger, Ranjit Ganguly, who was travelling to Mumbai for a holiday with his family, said he had been thrown from his carriage by the impact but his daughter and son were trapped inside.

Paramedics treated the injured beside the track, while the most serious cases were evacuated by air force helicopters.

The incident occurred at around 1:30 am (2000 GMT Thursday) in West Midnapore -- a Maoist stronghold around 135 kilometres (85 miles) west of Kolkata.

More than 80 passengers were taken to Kharagpur Railway Hospital where medical staff were overwhelmed by the number of wounded, some of them with serious head and spinal injuries.

"We just aren't set up for something like this," said hospital director Vivekanondo Mishra.

West Bengal Chief Minister Buddhadeb Bhattacharya said the attack warranted a review of the government's counter-insurgency strategy.

"We have to find ways to counter the Maoist menace. Innocent people are being killed," he told a press briefing in Kolkata.

The government launched a coordinated offensive, dubbed Operation Greenhunt, against the rebels in November 2009 with more than 60,000 paramilitary and state police.

The operation has produced few tangible results and the Maoist attacks have continued unabated, triggering growing calls for the army to be brought in.

Home Minister P. Chidambaram -- who has borne the brunt of public criticism over the handling of the insurgency -- recently acknowledged that changes were needed.

Hours after the train attack, Chidambaram held a pre-scheduled meeting with the head of the army, General V.K. Singh.

The Maoist rebellion, which Prime Minister Manmohan Singh has labelled the biggest threat to the country's internal security, began in West Bengal in 1967 and has since spread to 20 of India's 29 states.

In April, the rebels ambushed and killed 76 policemen in the central state of Chhattisgarh.