Zimbabwe is failing to meet its democratic obligations in the run up to polls on 29 March, a rights group says.
Zimbabweans queue to get into a Mugabe rally in Gweru
Human Rights Watch (HRW) says the government has intimidated opposition supporters, and that the electoral process is deeply flawed.
The US-based group says the Zimbabwe Electoral Commission (ZEC) is inadequately prepared to run the poll.
But the government said such reports reflected what the West wanted to hear and not what was actually happening.
"We are not surprised at all by these kind of reports, actually they are becoming a joke," Deputy Information Minister Bright Matonga told the BBC's Focus on Africa programme.
"The organisation that is doing that - they should be ashamed of themselves because they don't see anything positive about Zimbabwe."
The ZEC has announced that 5,934,768 people have registered to vote in 8,998 polling stations.
The opposition say they have found evidence of dead people registered to vote including a former minister who died 30 years ago.
They have gone to court seeking an electronic copy of the register to allow computerised searches and the easier detection of any fraud.
President Mugabe's main challengers in the presidential polls are the opposition Movement for Democratic Change's Morgan Tsvangirai and former Finance Minister Simba Makoni.
The Zimbabwe Election Support Network says the distribution of polling stations have been biased in favour of rural areas where Mr Mugabe has more support.
This could lead to urban supporters unable to cast their vote, it said
Mr Matonga dismissed the report's accusations that the ZEC was sympathetic to the government.
"The Zimbabwe Electoral Commission is comprised of persons from the ruling Zanu-PF and the opposition MDC," he said.
"You can't make a prejudgement on something that has not been proved wrong."
In a campaign rally on Tuesday, Mr Mugabe told supporters that 5,000 generators will be stationed at polling stations across the country in case of power cuts and to enable voting to continue until 7pm.
Mr Mugabe also told the rally in Gweru, south of the capital, that his government was considering taking punitive measures against British residents in Zimbabwe because of UK sanctions on Zimbabwe, AP news agency reported.
In the past, the government has pointed to a series of new laws designed to deal with electoral criticisms.
But HRW says those laws have either come too late to make any difference, or been selectively applied.
It accuses the security forces of intimidating and torturing opposition supporters, and state media of blatantly biased election coverage.
"Despite some improvements on paper to the election regulations, Zimbabweans aren't free to vote for the candidates of their choice," said HRW.
The report concludes that there is little chance that the polls will either establish democracy in Zimbabwe, or bring an end to the country's ongoing political crisis.
The opposition MDC said that the police had refused them permission to hold a rally at a Harare stadium because it was booked by Zanu-PF for four days in a row.
"It is impossible for a political party to hold a rally at the same place for four consecutive days and the decision by the police to turn down the MDC rally on such suspicious grounds is part of the rigging process," the MDC said in a statement.
Observers say administrative preparations for the polls are also being severely hampered by the nation's deepening economic crisis, with inflation running at more than 100,000% and shortages of fuel and basic foodstuffs.