DHAKA - Bangladesh opposition leader Khaleda Zia on Wednesday proclaimed her innocence on the eve of a verdict that authorities fear could spark violence if the former prime minister is jailed for corruption.

Police have banned street protests and rounded up what opposition figures say is thousands of their supporters in a crackdown ahead of Thursday's court ruling in the capital Dhaka.

A guilty verdict could prevent Zia, a former ally turned arch-nemesis of Prime Minister Sheikh Hasina, from contesting a general election slated for December.

Prosecutors are seeking life imprisonment for Zia - a two-time former prime minister and head of the Bangladesh Nationalist Party - for allegedly embezzling 21 million taka ($252,000) through a charity trust fund.

On the eve of the verdict the 72-year-old decried the charges as "false" and insisted "not a penny" had been stolen.

"This is an attempt to use the court against me, in an effort to sideline me from politics and elections and to isolate me from the people," Zia told a packed news conference. "I am ready to face all outcomes. I am not afraid of jail or punishment. I am not going to bow down my head."

Her party's spokesman Rizvi Ahmed told AFP that "approximately 3,500" opposition activists and officials had been arrested in a sweep by police and other security forces.

A former minister has been detained and a senior official has vanished, raising fears that security forces could be "disappearing" key opposition figures in the lead-up to the verdict.

The national police chief described the arrests as "routine work". Political demonstrations by Zia's centre-right BNP and its Islamist allies in 2014 and 2015 left nearly 200 people dead.

The BNP boycotted 2014 polls in which Hasina was re-elected but is expected to contest the upcoming general election.

Zia faces dozens of separate charges related to violence and corruption. Her son Tarique Rahman, who is in exile in London, is a co-defendant in the case. He was convicted of money-laundering in 2016.

Last month prosecutors sought the death penalty for Rahman over his alleged role in a deadly 2004 grenade attack that injured Hasina.