Bangladesh's Awami League party and its allies have said they will boycott forthcoming parliamentary elections.
Sheikh Hasina says the caretaker government is biased
The leader of the Awami League, Sheikh Hasina, said the atmosphere was not conducive to a free and fair election.
Alliance leaders say the caretaker government, led by President Iajuddin Ahmed, is biased in favour of the rival BNP which governed until October.
The boycott announcement has put a question mark over the election, scheduled for 22 January.
Correspondents say that Sheikh Hasina is unlikely to revoke her boycott decision, which will almost certainly lead to renewed political uncertainty and street protests.
Sheikh Hasina said that the caretaker government, led by President Iajuddin Ahmed since October, was biased in favour of her alliance's opponents.
More protests would seem to be inevitable
She said that fair elections would be impossible under the caretaker government.
"Mr Iajuddin Ahmed, who has become the chief adviser [of the caretaker government], wants to hold an election using an illegal voters' list," she told a news conference in Dhaka.
"We cannot view such an election as legitimate. That is why we, on behalf of the grand alliance, have decided not to participate in the staged election."
Sheikh Hasina, a former prime minister, said that while Mr Ahmed could stay as president, he should resign as head of the caretaker government.
The Awami League and its allies have called for a transport blockade throughout the country on 7 and 8 January to demand electoral reforms.
At least 45 people have been killed and hundreds injured in political violence since the caretaker government took over.