At least seven people have been killed in a petrol bomb attack on a bus in eastern Bangladesh.

The victims burned to death while at least another 16 people were left injured, Reuters reported.

The attack took place near the town of Chauddagram.It is the latest on a long line of blasts, carried out by opposition supporters, as political turmoil is growing in the country due to tensions between supporters of Prime Minister Sheikh Hasina and the main opposition leader Khaleda Zia.

"Seven died on the spot after opposition activists hurled petrol bombs," said fire department official Monir Hossain to reporters in the south eastern district of Comilla.

At the end of January, anti-government protesters firebombed several vehicles in the capital Dhaka and surrounding districts.

Zia, whose Bangladesh Nationalist Party (BNP) boycotted last year's elections, has demanded Hasina to step down.

However, Hasina refused and retaliated by arresting opposition leaders and anti-government protesters and banning all protests in the capital.

It is believed that at least 7,000 anti-government protesters have been arrested since 5 January 2014.

Tensions culminated in renewed violence between December 2014 and January 2015, during the first anniversary of the election.

Zia was threatened to be charged with murder after a protest during the election anniversary caused some deaths.

It is believed that Zia instigated protests that led to the torching of a vehicle that left three people severely injured.