The United Nations on Friday called on Bangladeshi police to refrain from excessive use of force amid recurring violence and mass arrests ahead of general elections.

The UN human rights office on Monday lamented the violence that has erupted at opposition rallies in recent months, with police using rubber bullets, tear gas and water cannons.

"Police, alongside men in plain clothing, have been seen using hammers, sticks, bats and iron rods, among other objects, to beat protesters," spokesman Jeremy Laurence told reporters in Geneva.

"Many opposition supporters, as well as some police, have been injured," he said, adding that "senior opposition leaders have been beaten in broad daylight, and their homes raided by people claiming to be law enforcement."

"Hundreds of opposition leaders and supporters have been arrested before and during the rallies."

Bangladesh's next general election is due before the current parliament's term expires in January.

The opposition Bangladesh Nationalist Party and dozens of smaller allies have called for protests throughout the country demanding Prime Minister Sheikh Hasina step down and the polls take place under a neutral caretaker government.

Hasina has rejected the demand, saying it is unconstitutional.

Laurence stressed that Bangladeshi authorities "must abide by their human rights obligations and allow people to exercise their rights to freedom of peaceful assembly and freedom of opinion and expression."

They must also "act diligently to protect against attempts by third parties to suppress or limit exercise of those rights", he said.

The UN rights office, he said, was calling on "police to ensure that force is only used when strictly necessary", insisting that any "excessive use of force must be promptly investigated, and those responsible held to account."

Laurence also called on the authorities to ensure that those canvassing ahead of the elections were assured "a safe and peaceful environment that respects and promotes political plurality and the expression of diverse views, in full respect for fundamental rights and freedoms."