A leading human rights group has accused Azerbaijan's government of systematic intimidation and violence ahead of parliamentary elections.
Tensions have boiled over ahead of the 6 November election
New York-based Human Rights Watch says action against opposition supporters has "extinguished the possibility of free and fair elections".
The group lists mass arrests, beatings and other forms of intimidation.
Last week, a former aide to President Ilham Aliyev and the head of a major company was arrested on coup charges.
They were accused of planning a coup with opposition leader Rasul Guliyev who says the government has been trying to make it difficult for him to return to Azerbaijan to contest the election - a charge Baku denies.
More than 20 Azeri officials have been arrested or sacked in recent weeks on suspicion of supporting Mr Guliyev.
Plea for fairness
The Human Rights Watch document, published on Monday ahead of the 6 November elections, says police violence and arbitrary arrests against opposition activists have been endemic during the campaign period.
"People cannot vote freely in an election when the authorities are beating up opposition supporters and preventing candidates from campaigning," said Holly Cartner, Europe and Central Asia director at Human Rights Watch.
"Azerbaijan's history of election fraud and abuse is threatening to repeat itself."
Presidential elections in 2003, which resulted in Ilham Aliyev succeeding his father, Heydar, was followed by violence, as riot police clashed with opposition supporters who accused the government of rigging the election.
Observers from the Organization of Security and Co-operation in Europe (OSCE) also denounced the poll, saying that it had not met international standards.
Human Rights Watch has called on Azerbaijani government to "immediately stop harassing opposition and independent activists, to allow freedom of assembly and to desist from intimidation on election day".
Last week, state television reported that President Aliyev had eased restrictions on foreign observers monitoring the elections.
Non-governmental organisations that receive most of their funding from abroad will now be able to send their workers to observe the vote.
The president has reportedly also ordered indelible ink to be used to mark voters' fingers, reducing the risk of voting irregularities.
The US recently expressed concerns that the November polls would not be fair.