At least 34 people have been killed in firebomb attacks amid political unrest in Bangladesh.

The attacks, in which dozens were also injured, were carried out at the weekend as tensions are rising between supporters of Prime Minister Sheikh Hasina and the main opposition leader Khaleda Zia, Reuters reported.

Anti-government protesters firebombed several vehicles in the capital Dhaka and surrounding districts, witnesses said.

Police said at least 25 people died in arson attacks, including two on Friday. Eight more were killed in clashes with police, and one died following injuries from a crude bomb blast, they added.

"Nine are in critical condition," said Mohammad Sajjat Khandakar, a doctor at Dhaka Medical College Hospital.

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.

Referring to the BNP, Health Minister Mohammed Nasim said: "They should immediately stop the killing of innocent people, children, woman, laborers."

Worldwide leaders have expressed concern over growing unrest in the country and have urged Zia and Hasina to engage in dialogue in order to halt the violence.