Bangladesh Nationalist Party official Abdul Moyeen Khan told Reuters he hid out in different people's homes until nominations closed.

"They were already hunting the opposition leaders in particular in their homes... 25,000 of our party leaders and workers starting from our secretary general down to the grassroots level have been taken into custody."

Khan says the arrests took place in late October, after deadly anti-government protests leading up to the election, as incumbent Prime Minister Sheikh Hasina chases a fourth straight term.

Khan's party is boycotting the vote over Hasina's refusal to cede power to a caretaker government to run the poll.

Hasina and her Awami League have repeatedly condemned the BNP as troublemakers out to ruin the elections.

They also rebuffed reports by rights groups Amnesty International and Human Rights Watch that said the government was trying to subdue the opposition.

According to Afroza Abbas, head of the BNP women's wing, about 100 female members have been arrested over the past four to six weeks.

"The January 7 polls will be a one-party event," she said.

Her husband is among the BNP's top decision makers, who's been in jail since November 1.

BNP officials say police ransacked the homes of party leaders and workers in frequent nighttime raids.

But police say they've arrested only those involved in the violence.

In November, New York-based Human Rights Watch put the number of arrests of BNP activists at 10,000, with two police officers among at least 16 dead and about 5,500 injured in the violence.

The U.S. has condemned the violence and curbed visas for Bangladeshis believed to have a role in undermining elections, including members of law enforcement, the ruling party, and the political opposition.

Researcher Amit Ranjan, from the National University of Singapore's Institute of South Asian Studies, said

although violent suppressions of dissent was common in Bangladesh, the recent government steps were unprecedented.

"What they believe in, they are fully looking at how they are going to stay in power."

The crackdown comes at a time when the opposition leadership finds itself in disarray.

Ailing party president Khaleda Zia, a long-time rival of Hasina's, has kept out of active politics.

Zia's son has taken the mantle for now, but is in exile.

And the party's next most senior leader has been in jail since late October.