Opposition supporters set fire to at least six buses in Bangladesh's capital on Saturday, the eve of a nationwide anti-government strike, police said.
Several people were injured in the attacks, a police official said on condition of anonymity because he was not authorized to speak to the media. He gave no further details.
Opposition groups, led by former Prime Minister Khaleda Zia, are calling for the dawn-to-dusk general strike on Sunday to protest government moves to amend the constitution. The government wants to repeal a provision that requires it to hand over power at the end of its term to a nonpartisan caretaker administration to oversee elections.
The opposition accuses the government of attempting to cling to power after its five-year term ends in 2014. The government denies the allegation.
Dhaka police Commissioner Benazir Ahmed says thousands of security personnel were being deployed in the capital and elsewhere to prevent violence. Schools, stores and transport lines are expected to be closed.
The South Asian nation has a history of political violence, and opposition groups commonly enforce general strikes to highlight their demands.
Under the constitution, prime ministers must step down after a five-year term to allow a nonpartisan administration to conduct new polls in three months. A former chief justice is usually chosen to head the caretaker administration.
Prime Minister Sheikh Hasina's government has recently said the caretaker provision should be repealed because it puts an unelected government in power.