Dhaka: Bangladesh police Wednesday charged opposition leader Khaleda Zia with "instigating" a deadly bus firebombing as four more people were killed -- allegedly by security forces -- amid spiralling political unrest.
Police laid initial charges against the former two-time premier over Tuesday`s attack which killed seven people in the eastern town of Chauddagram, the deadliest since the month-long protests started.
"She has been named as an instigator of the attack. At least 56 other people were also charged in the case," district police chief Tutul Chakrabarty told AFP.
Police also arrested around a dozen protesters, accusing them of carrying out the attack as part of an opposition-led nationwide transport blockade.
The charges are the latest for 69-year-old Zia. Police said last week she was under investigation for "abetting" and "instigating" other recent firebombings.
There was no immediate comment from Zia or her Bangladesh Nationalist Party (BNP), which has condemned Tuesday`s attack and denied its supporters were responsible.
Authorities have stepped up pressure on Zia, who has been holed up in her office since January 3, to try to halt the violence.
Four more people were killed -- two suspected saboteurs were shot dead by an elite force in Dhaka and two young BNP activists died -- as the unrest worsened.
Police said the two activists were crushed under a moving truck as they tried to firebomb the vehicle Tuesday. Relatives said the two were arrested by police a day before and were tortured to death.
At least 58 people have now been killed -- mostly victims of firebombings of buses, cars and lorries -- as activists try to enforce the blockade of roads, railways and waterways.
Zia called the protests early last month to try to force Prime Minister Sheikh Hasina to call a fresh general election. The BNP and its allies boycotted the January 2014 poll as they believed the result would be rigged.
Security forces have launched a nationwide crackdown, arresting more than 10,000 opposition activists since the blockade began.
Hasina has accused Zia of trying to trigger "anarchy" and ordered security agencies to hunt down protesters.
The EU, the nation`s biggest export destination, has urged the government and opposition to hold talks to resolve the crisis.