Bangladeshi officials say at least 50 people were injured during clashes between police and opposition activists in the capital.
Police fired tear gas to stop thousands of demonstrators from marching to the secretariat, which houses government ministries.
Witnesses say activists threw stones at police and destroyed vehicles during Thursday's demonstration in central Dhaka.
The main opposition Awami League and its 13 allies organized the rally to demand electoral reform ahead of the country's next elections scheduled for 2007.
The opposition is calling for the resignation of three election commissioners it accuses of being pro-government.
Prime Minister Khaleda Zia's government came to power in 2001. She vows to hold the office until the end of her five-year term in October. Some information for this report was provided by AFP, AP and Reuters.