Homemade bombs have exploded in Bangladesh's capital and police fired tear gas at demonstrators as opposition parties enforced a general strike, demanding that the government restore an election-time caretaker administration.
Schools and businesses were closed in Dhaka and other major cities and towns during the eight-hour shutdown. Nationwide transportation was largely disrupted during the second opposition strike this week.
Witnesses and TV stations reported that police fought pitched battles with opposition activists in parts of Dhaka, but it was not immediately clear if anyone was injured. Several vehicles whose drivers tried to defy the strike were either torched or smashed, police said.
Bangla Vision and Massranga television stations said dozens of people were detained in major cities.
A coalition of 18 opposition parties was enforcing the strike to demand that the caretaker government be restored before the next national elections due in 2014. A key coalition partner is also pressing for freedom of its leaders facing charges of crimes against humanity involving the 1971 independence war against Pakistan.
Jamaat-e-Islami, the country's largest Islamic party and the main partner of Mr Zia's party, has been demanding the release of nine of its leaders facing charges of crimes against humanity. Two other leaders from Mr Zia's party face similar charges and are in jail. Mr Zia has criticised the trial, calling it politically motivated.
Jamaat-e-Islami leaders are accused of abetting the Pakistani army in killing and raping during the war. The party says the charges are aimed at weakening it.
Mr Zia's party demanded the release of a senior leader who was arrested on charges of instigating violence earlier this week.
The government of prime minister Sheikh Hasina last year scrapped the 15-year-old caretaker government system during elections following a Supreme Court ruling that the constitution allows only popularly elected governments. Opposition parties fear the election will be rigged if the current party remains in power.