Nine people were killed and 30 injured in Bangladesh after firebombs were thrown on a crowded bus and truck late Friday night and Saturday morning, according to local authorities.

Police blamed opposition activists for the attacks. Violence has flared amid anti-government protests over the past month, resulting in at least 70 deaths and hundreds of injuries.

Dozens have been killed in similar firebombings that have taken place throughout Bangladesh in recent weeks. The government has responded with force, arresting thousands of opposition activists and killing dozens in police operations.

Prime Minister Sheikh Hasina said that "as the head of the government, I'm giving [the police] the liberty to take any action wherever and whenever it will be deemed necessary" to stop the attacks.

Video shows the aftermath of a firebomb attack on a bus in the southern Bangaldesh village of Chauddagram.

Bangladesh has been mired in a political crisis for much of the last year, centered on a long-standing rivalry between the Bangladesh Nationalist Party (BNP), led by Khaleda Zia, and the ruling Awami League, led by Hasina. The position of prime minister has alternated between Zia and Hasina for nearly 20 years.

The BNP boycotted last year's election, claiming it was rigged. The party has since called for Hasina's ouster. The anti-government protests began in January on the first anniversary of the contentious election. Opposition activists have since shut down roads and railways, and imposed general strikes. The government has arrested more than 7,000 opposition activists.

Amnesty International criticized the Bangladeshi government for responding to the opposition with brute force, warning that the tactic risks exacerbating the cycle of violence.

Abbas Faiz, Amnesty International's Bangladesh researcher, issued a statement addressing Hasina's comment about allowing police to crackdown. "Remarks like these carry a high risk of being seen as an open invitation for the police to use unnecessary and excessive force against demonstrators or even to carry out extrajudicial executions — which Bangladeshi security forces have carried out with appalling frequency in the past," Faiz said.

The BNP has called for a 72-hour general strike starting Sunday. Leaders are demanding the closure of schools and businesses across the country.

The United States condemned today's petrol bomb attack. "There is simply no justification for such actions in a democratic Bangladesh," State Department spokeswoman Marie Harf said in a statement.

"We deplore the unconscionable attacks including bus burnings, throwing incendiary devices, and train derailments that have killed and wounded innocent victims," Harf added.