Thousands of police officials have fanned out across Bangladesh's capital ahead of a mass opposition rally calling on Prime Minister Sheikh Hasina to cancel next month's elections.
Hasina's rival, former Prime Minister Khaleda Zia, is expected to address the rally Sunday in defiance of a government ban on large political gatherings.
Media reports say more than 650 people have been detained since Friday as part of a nationwide crackdown following months of unrest ahead of Jan. 5 elections, which the opposition is boycotting. Opposition parties say those detained are their activists.
The opposition insists Hasina should resign and hand over power to an independent caretaker to oversee the polls.
More than 150 people have died in the political violence since October.