Polling booths have been set on fire in Bangladesh on the eve of general elections. On Friday four people, including two children, died in an apparent arson attack on a train in Bangladesh. Police said they had arrested seven people in connection with the incident. The fire on the passenger train, which raced through four coaches, was aimed at scaring people before the vote, a police official said, though authorities did not immediately name any individuals or groups as suspects. Violence is common during Bangladesh elections and Sunday’s voting comes amid an increasingly polarised political culture led by two powerful women: the prime minister, Sheikh Hasina, and the former prime minister, Khaleda Zia, an opposition leader who is under house arrest. Zia’s Bangladesh Nationalist party and other opposition groups are boycotting the vote, saying it would not be free or fair under Hasina. They had demanded she step aside and let a neutral caretaker government administer the polling, but her government insisted there was no provision in the constitution for such a move. The fire on the train broke out as it was travelling towards Dhaka’s main railway station at about 9pm, Rakibul Hasan, a duty officer of the Fire Service and Civil Defence, said. At least four bodies were recovered from inside the train, police told reporters at the scene. Mahid Uddin, an additional police commissioner with the Dhaka Metropolitan police, said the fire was “clearly an act of sabotage”. Seven firefighting units were sent to the scene to douse the blaze, Hasan said. Campaigning for the elections officially ended on Friday morning. The Election Commission announced polling would be held in 299 of the 300 constituencies on Sunday. The election in one constituency was postponed after an independent candidate died of natural causes. Ruhul Kabir Rizvi, a senior joint secretary general in Zia’s party, has urged people not to vote on Sunday and called for a 48-hour general strike from 6am on Saturday to 6am on Monday. On Friday morning, Rizvi led more than 100 opposition leaders and activists holding sticks and chanting anti-government slogans as they marched in the capital’s Karwan Bazar area. “People will not accept this illegal election. People will not accept this election of looters,” Rizvi said during the march. Hasina addressed the nation in a televised campaign speech on Thursday night, urging people to head to ballot stations. “If I have made any mistakes along the way, I ask your forgiveness. If I can form the government again, I will get a chance to correct the mistakes. Give me an opportunity to serve you,” she said. At least three people have been killed in violence attributed to political clashes since the campaign officially began on 18 December. The UN secretary general’s associate spokesperson, Florencia Soto Nino, said in New York on Wednesday: “We are watching the process closely, and we hope that all elections happen in a transparent and organised manner.” Nearly 1.6 million people – half of them security personnel – will oversee the election, with 119.1 million registered voters eligible to cast their ballot in more than 42,000 polling stations, the commission said. Troops have been deployed across the country to assist when needed under the supervision of magistrates, a common practice in Bangladesh during general elections.