Foreign Minister AK Abdul Momen has termed the deadly arson attack on the Benapole Express as an "unforgivable crime against humanity".

Four people, including a woman and her child, were burnt alive and several others injured as a blaze ripped through the train near Dhaka's Gopibagh on Friday night. Eight others are fighting for their lives at the Sheikh Hasina National Institute of Burn and Plastic Surgery.

The incident occurred on the eve of the BNP's nationwide hartal aimed at disrupting the Jan 7 election.

"This reprehensible incident, undoubtedly orchestrated by those with malicious intent, strikes at the very heart of our democratic values," Momen said on Saturday.

Questioning the timing of the tragedy, the foreign minister described the incident as a "deliberate" act of sabotage intended to "hinder the festivity, safety and security" of the electoral process.

"It is an affront to democracy, an attack on the democratic process, and a grave violation of the rights of our citizens."

The BNP and other like-minded parties are campaigning for a boycott of the election after enforcing a series of shutdowns and blockades over the last two months to press for the institution of a pre-election caretaker government.

Around 300 vehicles have been vandalised amid the BNP's protest programmes, while at least five people died in incidents of railway sabotage.

"This act of setting a train on fire, with people burning inside is characteristic of the pattern of violence that we have witnessed before as well. This has shocked the conscience of our whole society - and indeed - the whole world," said Momen.

He assured that everyone involved in the "heinous crime" would be brought to justice.