Explosions of home-made bombs have been reported across the capital of Bangladesh as opposition activists enforcing a day-long general strike rioted and clashed with police.
Police fired tear gas to disperse crowds of people who were smashing vehicles.
It was not immediately clear if anyone was injured in the violence described by witnesses and television reports in parts of the capital, Dhaka.
A coalition of 18 opposition parties was enforcing the strike to demand that a caretaker government be restored before the next national elections due in 2014, while a key coalition partner wants their leaders, who are facing charges of crimes against humanity, to be freed from jail.
Schools and businesses remained closed in Dhaka and other major cities and towns and transportation was disrupted across Bangladesh, a parliamentary democracy that has a history of fierce political violence.
Amid the violence, the United States urged the two main political parties to resolve their disputes through dialogue.
Independent television reported the detention of at least six opposition activists from the Dhaka University area.
Police said activists torched at least 21 vehicles in Dhaka after police arrested a senior leader of the main opposition Bangladesh Nationalist Party, led by former prime minister Khaleda Zia.
The opposition said it would enforce another general strike tomorrow unless those detained during the violence are freed by today.
An opposition spokesman said at least 250 people were detained during the strike.
The government of Prime Minister Sheikh Hasina scrapped the 15-year-old caretaker system last year in line with a Supreme Court order that ruled it unconstitutional, saying the constitution allows only popularly elected people to run the government.
Opposition parties fear the election will be rigged if the current party remains in power.