Bangladesh police have formally charged Begum Khaleda Zia, head of the opposition Bangladesh Nationalist Party (BNP) with instigating a petrol bomb attack on a passenger bus, a senior police official said on Sunday.
Police said 29 people suffered burns in the incident on Friday and nine passengers are in critical condition.
The authorities accuse the BNP leader of ordering the attack as part of the party's campaign to blockade Dhaka to try to force a general election.
"She was charged for the first time with instigating such an attack on a passenger bus during the ongoing blockade programme," Habibur Rahman, Superintendent of Polices of Dhaka, told Reuters.
One senior leader of the BNP, Rizvi Ahmed, denied the allegations against Khaleda, who is not in custody but still working in her office.
The BNP has been blockading Dhaka since January 6 to try to compel the government of Prime Minister Sheikh Hasina to hold an election. The party boycotted a vote in 2014.
Police say they have arrested scores of BNP activists since the blockade began for various offences connected to the campaign, but the BNP says about 10,000 people have been taken into custody.
Bangladesh has been racked by political violence for decades, and the latest crisis erupted on January 5 when demonstrations broke out on the anniversary of last year's disputed elections.
The office of prime minister has been held by Hasina or the BNP's Khaleda for all but two of the past 23 years and the rivalry between them is bitter.
At least 34 people have died in Bangladesh and scores have been injured, most of them in fire bomb attacks, amid rising political unrest fuelled by a stand-off between the two of them.
The renewed political turmoil could cause a delay in shipments by the country's $24-billion garment industry, already under pressure after a string of fatal accidents.
The opposition called for another 36-hour countrywide strike from Sunday morning to protest against the arrests and "oppression" of its leaders.
The United States, the European Union and Britain have voiced concern and urged all Bangladeshi parties to engage in dialogue.
Police announced a 500,000 taka ($6345) reward if anyone can help to identify or hold the culprits who threw the petrol bomb on Friday.