Bangladesh's main Opposition BNP has demanded a UN-supervised investigation into a fire on a passenger train that killed four persons, calling it a "pre-planned" act of sabotage ahead of the general elections being boycotted by the party.

The incident happened around 9 pm on Friday when four carriages of the Benapole Express that runs from Benapole, a town bordering the Indian state of West Bengal, were set on fire as it nearly reached its destination of the capital’s Kamalapur Railway Station.

Railway officials said that most of the train’s nearly 292 passengers were returning home from India.

Shahjahan Sikder, deputy assistant director of the Fire Service and Civil Defence Media Cell, said they recovered four bodies from the gutted coaches of the train.

In a statement, Bangladesh Nationalist Party (BNP) senior Joint Secretary Ruhul Kabir Rizvi expressed concern over the "heartbreaking incident of casualties due to arson by miscreants on the Benapole Express train headed from Benapole to Dhaka".

"There is no doubt that the Benapole Express train fire was an act of sabotage, leading to the loss of life," The Daily Star newspaper quoted Rizvi as saying.

He termed it an "inhuman brutal atrocity against humanity" and called for a UN-supervised investigation into the incident, the paper said.

Rizvi said that the incident was "pre-planned" and called for the immediate arrest and punishment of the "perpetrators involved".

Prime Minister Sheikh Hasina expressed deep shock and sorrow at the loss of four lives in the Benapole Express train fire. She directed the authorities concerned to investigate whether the fire was an act of sabotage.

She also prayed for the salvation of the departed souls and directed the authorities to take immediate steps for the treatment of the injured.

Bangladesh goes to polls on Sunday. More than 100 foreign observers, including three from India, have reached Dhaka to monitor the general election.

Led by former prime minister Khalida Zia, the BNP is boycotting the general election and it is demanding an interim non-party neutral government to hold the election.

The demand was rejected by the government headed by Prime Minister Hasina, who is heading the ruling Awami League.

Foreign Ministry officials said a three-member delegation from the Election Commission of India reached Dhaka on Friday while 122 others from different countries were set to be here ahead of the January 7 polls, which the United Nations said would watch closely.

Bangladesh witnessed a couple of train-related arson incidents in recent months.

Unidentified person on December 19 set a train ablaze killing four people, among them a mother and child, amid an opposition called countrywide strike on that day.

One passenger was killed and dozens wounded as saboteurs uprooted railway tracks when seven carriages derailed in Gazipur on the outskirts of the capital in early December.

On January 2, a train carrying some 300 passengers narrowly averted a major crash at the last minute as suspected saboteurs removed 28 dog spikes or hooks from the tracks on a railway bridge in northern Bangladesh.

Awami League accused the BNP of carrying out the sabotage, which the party denied.

A school was partially damaged after miscreants set it on fire in Khulna's Dumuria upazila on Friday night.

Officer-in-Charge of Dumuria Police Station Sukant Saha said miscreants set fire to Tipna Government Primary School in Kharnia Union around 9:30 pm thinking it was a polling station.

The school library was burnt due to the fire.

"We are conducting drives to arrest the miscreants," he added.

Unidentified miscreants also partially burnt a passenger bus in the port city's Nayabazar-Eidgaon area on Friday night. However, no casualty was reported.

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