The New York-based human rights group, in a report on Wednesday, also accused Angola's government of meddling in the electoral commission and said such behaviour threatened the chances of a fair ballot on September 5.

"(Human Rights Watch) should not interfere in the internal matters of Angola," MPLA spokesman Norberto dos Santos told Reuters on Thursday.

"What they said in the report is offensive and has no basis of truth. We know Human Rights Watch hatred towards the Angolan people. All that I ask is that they stop interfering with the electoral process."

Angola's main opposition party UNITA -- who lost a brutal 27-year civil war against the government in 2002 -- accused the MPLA of attacking a group of their supporters in the central province of Huambo on Wednesday.

"More than 100 MPLA supporters carrying machetes, stones and sticks attacked members of a UNITA delegation campaigning in Londuimbali, the province of Huambo," Alcides Sakala, a senior member of UNITA in charge of the campaign, told Reuters.

The scuffles ended when police fired shots into the air, a police officer was quoted by the Portuguese news agency Lusa as saying. There were no reports of deaths or serious injuries.

Angola's government has denied accusations of rights abuses. When asked about the Human Rights Watch report, Prime Minister Fernando Dias Dos Santos said on Wednesday the polls would take place in a "free, fair and transparent" environment.

The official election campaign kicked off on August 5 with 10 parties and four coalitions competing for votes.

But the recent events could threaten Angolan president Jose Eduardo dos Santos' intention of having the oil-rich nation's first national vote for 16 years set an example on the continent after flawed polls in Kenya and Zimbabwe.

His MPLA party, in power since Angola's independence from Portugal in 1975, is widely expected to retain its majority in the 220-member parliament.

A total of 5,198 candidates will vie for seats in a country that rivals Nigeria as Africa's biggest oil producer but where two thirds of the population live on less than $2 a day.

A presidential ballot is expected to take place in 2009.