seen as a crucial step to building democracy after nine years of war but which many fear will be marred by fraud and insecurity.
"We call on our Muslim nation to boycott this process and thus foil all foreign processes and drive away the invaders from your country by sticking to jihad and Islamic resistance," the Taliban said in a statement.
A deadly campaign of violence and intimidation against parliamentary candidates and supporters has catapulted security to the top of concerns surrounding the vote.
Around 10.5 million Afghans are eligible to vote for the lower house of parliament, the Wolesi Jirga, in the second poll of its kind since the Taliban were ousted in the 2001 US-led invasion and only the second in 40 years.
Despite some calls for the election to be cancelled because of poor security and the spread of the insurgency to once relatively stable areas, Afghan and Western officials said an imperfect vote would be better than none at all.
The ballot is being held more than a year after the fraud-tainted election that returned Western-backed President Hamid Karzai to power for a second five-year term.
Styling themselves as "the Islamic Emirate of Afghanistan," as they did during their 1996-2001 rule, the Taliban said they were "striving to foil these colonialist plans of the invaders including this deceptive process with the help of Allah and your Muslim countrymen".
They said militants had "already chalked out certain measures... to frustrate this American process and will implement them on the day when the illegitimate process is conducted".
The hardline Islamist militia warned last month that anyone associated with the vote was a target and have waged dozens of attacks, killing three candidates and five campaign workers.
Around 250,000 Afghan soldiers, police and intelligence agents, backed by NATO troops, will provide security on polling day, which has been declared a national holiday.
"We're on track," Afghan army operations chief General Afzal Aman said.
More than 2,500 candidates are vying for 249 seats, including 68 reserved for women, who have been a particular target of intimidation.
But the future make-up of parliament will little alter the nature of government in Afghanistan, where power is largely concentrated in the hands of Karzai, who is kept in office by 150,000 US-led foreign troops.
Of 5,816 polling centres, more than 1,000 located mostly in Taliban heartlands in the south and the east will not open because officials said safety in those areas cannot be guaranteed.
The UN denied a report it had evacuated 300 staff ahead of the elections, after the organisation lost at least five workers -- all of them working on the presidential vote -- in a Taliban attack on their guesthouse last October.
Spokesman Kieran Dwyer told AFP that 170 extra staff had been brought into the country to "provide technical and logistical support" for the vote, but that other international staff not involved had been told to take holidays.
As the war has become entrenched, Taliban presence has spread from their southern heartland to previously peaceful regions in the north and west.
Western officials acknowledge that Saturday's election is also likely to be marred by fraud and Taliban intimidation, which could keep turnout low, but observers believe it can only be an improvement on the 2009 presidential vote.
"The election will not be perfect," Staffan de Mistura, the UN's special representative to Afghanistan, told AFP.
But he said: "Ballots are a better way to solve issues than bullets."
The line-up of candidates -- many of them youthful first-timers -- promises to inject some new life into what is one of Afghanistan's few truly combative political institutions.
In cities across the country, almost every available inch of public space has been festooned with election posters showing photographs of the candidates and the symbol that will appear next to their names on the ballot paper.
With illiteracy rates close to 80 percent, candidates' mandatory symbols are crucial and include everything from horse shoes to flowers, vases, computers, books, prayer mats, pomegranates, birds and scales.
Preliminary results are expected on September 22 and final results are due on October 31.