Attackers have thrown petrol bombs on a packed passenger bus in Dhaka, leaving at least seven people dead and 16 others injured.

The attack, by an unidentified group, came amid a nationwide general strike enforced by an opposition alliance calling for new elections in Bangladesh.

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

He said the injured have been taken to hospital.

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