Police said at least seven people were burned to death and 15 others left injured after unidentified attackers threw petrol bombs on a passenger bus in Bangladesh on Tuesday. Passengers were asleep and en route to the capital city of Dhaka when the attack happened near the town of Chauddagram. The incident is the latest in a string of violence since anti-government protests erupted last month, when opposition leader Khaleda Zia launched a blockade of roads, railways, and waterways across the nation in attempt to force Prime Minister Sheikh Hasina to step down. Zia said her Bangladesh Nationalist Party (BNP) is not behind Tuesday’s attack. Authorities raided neighboring villages but no arrests have been made, police said. Bangladesh has arrested more than 7,000 opposition activists since protests began and at least 53 people have died, most from arson attacks, since Jan. 5.