Bangladesh Opposition parties planned a second day of road marches to the capital on Wednesday, despite a government warning of a possible attack by unidentified extremists.
Some 20,000 people marched to Dhaka on Tuesday on the first day of a campaign by a 14-party opposition alliance to force the government to implement electoral reforms ahead of a general election next year.
Leaders of the Awami League, which heads the alliance, said police had launched a countrywide crackdown on opposition activists, picking up nearly 2,000 over the last three days, in a bid to discourage the marches.
"But we are determined to hold all the six marches planned between July 25 to 30," said Abdul Jalil, the League's general secretary.
The government said there was information that the marches could be targeted by extremists. More than 4,000 extra police and troops have been deployed in the capital.
The government did not say from where the extremist threat came from but Islamist militants launched a series of bomb attacks across the country between August and December last year, killing at least 30 people and wounding 150.
"Stringent security measures would remain in force through the entire march plans by the opposition," said a senior police officer on Wednesday.
The opposition wants the removal of the chief election commissioner, whom it accuse of pro-government bias, and a say in choosing the chief of a caretaker administration that would supervise the election next January.
Today's 10 km march was likely to shut transport on one of the country's busiest highways linking Dhaka to Chittagong port, transport operators said, as opposition activists gather on the outskirts of the capital.