A police official says unidentified attackers have thrown petrol bombs on a packed passenger bus, leaving at least seven people dead and 16 others injured, amid a nationwide general strike enforced by an opposition alliance calling for new elections in Bangladesh.

Local police chief Uttam Chakrabarty says the attack took place early Tuesday in the eastern district of Comilla when passengers were asleep on a trip to the capital, Dhaka, from the southern coastal district of Cox's Bazar.

Chakrabarty says the injured have been hospitalized.

At least 53 people have died, mostly in arson attacks allegedly by opposition activists, since Jan. 5 as the opposition alliance led by former Prime Minister Khaleda Zia launched a nationwide transportation blockade to force Prime Minister Sheikh Hasina to step down.