At least three people burned to death when suspected anti-government protesters petrol-bombed a truck in the southern town of Gournadi on Saturday morning, local police chief Sazzad Hossain told AFP.

The death toll from a similar attack late Friday on a bus in the northern Gaibandha district rose to six after two more passengers died from their injuries on Saturday, police added.

One anti-government protester was also shot dead in a shootout with officers in the coastal town of Swarupkathi, police said.

The latest deaths brought the overall toll in the month-long unrest to at least 76, mostly victims of fire-bombings of buses and trucks.

The violence began after the government confined opposition leader Khaleda Zia to her office when she threatened to lead a mass rally on January 5, the first anniversary of a disputed polls.

Zia then called a nationwide blockade of transport to topple the government of Prime Minister Sheikh Hasina and pave the way for new polls under a neutral government.

The protests have become increasingly violent and nearly 1,000 vehicles have been torched or vandalised.

The security forces have in turn arrested more than 10,000 opposition supporters while more than a dozen protesters have been shot dead, prompting allegations of a shoot-to-kill strategy.

After a plea from the US State Department for an end to the “unconscionable” firebombings, Human Rights Watch issued a plea for a halt to the “bloodletting”.

“All parties should cooperate to stop the cycle of violent crimes and ensure those responsible for all crimes are arrested and prosecuted,” said the New York-based watchdog's Asia director Brad Adams.

“The violent crimes being committed by some members of the opposition cannot justify killings, injuries, and wrongful arrests by the government."

Zia has vowed to continue protests but Hasina has ruled out any polls until the end of her tenure in early 2019.