Opposition parties said the arrests since the election was called on November 8 were intended to create a 'climate of fear'.
Bangladesh police have arrested more than 10,500 opposition activists in a crackdown ahead of elections this week, opposition parties said Tuesday.
The figures were released after the United States urged Prime Minister Sheikh Hasina's government to do more to ensure free polls on Sunday when she is aiming to win a record fourth term.
Opposition parties said the arrests since the election was called on November 8 were intended to create a "climate of fear".
The main opposition Bangladesh Nationalist Party (BNP), whose leader Khaleda Zia is serving a 17-year jail term, said 7,021 of its activists had been detained.
Its Islamist ally, Jamaat-e-Islami, said more than 3,500 followers were in custody. Jamaat-e-Islami is banned from contesting elections but has candidates taking part as individuals with the BNP.
"Every day 80 to 90 of our activists have been arrested nationwide. These arrests have created a climate of fear," Jamaat secretary general Shafiqur Rahman told AFP.
Police spokesman Sohel Rana did not confirm any figure for arrests but said they did not make "unnecessary arrests" without warrants.
"We never target any individual unless they break the law. These people have specific warrants against them," he told AFP.
Rizvi Ahmed, a BNP spokesman, said the charges laid against party activists were "fictitious" and "ghost" cases" aiming for "a lopsided election" in favour of Hasina.
Hasina and Zia have been political foes since the introduction of democracy in 1991. They have traditionally alternated in power but Hasina's current rule has lasted since 2009 and Zia's jail term this year prevented her from taking part in the election.
The BNP and its allies have also accused police and ruling Awami League party activists of attacking their activists and candidates.
The BNP had hoped the deployment of 30,000 troops on Monday would improve security across the Muslim-majority majority country of 165 million.
"The Awami League activists along with the law enforcing agencies attacked our candidates at 28 constituencies (in the last 24 hours). Nineteen of our candidates and over 100 activists were injured in the attack,” Ahmed told a press briefing.
He said that since the election campaign started at least 152 BNP candidates were attacked and hundreds of activists were injured in clashes.
Police spokesman Rana denied police had attacked any opposition activists, acknowledging only that "isolated incidents" were possible.
"If we receive any clear and evident allegation against any police member, we will surely take stern action," Rana said.
Hasina won the 2008 poll by a landslide and the BNP boycotted the 2014 election — saying it was not free and fair — gifting her a return to power.
Civil society and rights groups have accused Hasina's government of silencing dissent and muzzling the press through a strict digital-security law.
The US State Department also raised concerns about Sunday's vote after it cancelled a planned observer mission by the Asian Network for Free Elections, which is funded by the US government because Bangladesh held up visas and credentials.
State Department spokesman Robert Palladino said democratic elections must have "space for peaceful expression and assembly, for independent media to do its job covering electoral developments, for participants to have access to information and for all individuals to be able to partake in the electoral process without harassment, intimidation or violence."
"We encourage the government of Bangladesh to uphold its commitment to a democratic process by ensuring all Bangladeshis are free to peacefully express themselves and participate," he added in a statement.