Two Afghan parliamentary candidates and 18 poll officials and campaign workers have been kidnapped in three separate incidents.
The Taliban are suspected of abducting the would-be MPs in eastern Laghman province and western Herat province.
The militants said they had seized the 18 poll officials and campaign workers in north-western Bagdhis province.
The Taliban have threatened to attack voters and election workers taking part in Saturday's parliamentary elections.
Washington is watching the poll closely, as US President Barack Obama prepares a war strategy review in December that is expected to consider the scale of plans to start withdrawing American troops from next year.
The poll is also seen as a test of credibility for Afghan President Hamid Karzai after last year's presidential elections, which he won despite a third of his votes being thrown out as fakes.
Security forces are setting up extra checkpoints across the country and are using sniffer dogs as they search every car heading along main roads into the capital, Kabul.
They are questioning anyone wearing a burka, as insurgents have previously hidden under the Islamic full-body robe to get past checkpoints.
A Taliban spokesman, Zabullah Mojahed, told the BBC they had kidnapped candidate Mawli Hayatullah in Laghman on Friday.
The militants also said they abducted the 18 poll officials and campaign workers in Bagdhis on Thursday.
It has also emerged that another candidate, Saifullah Mojadedi, was kidnapped in Herat by unknown armed men on Wednesday, according to the Electoral Complaints Commission.
The Taliban have been handing out letters warning voters to boycott the poll or risk reprisals.
Adding to concerns about fraud, police in Ningarhar province told the BBC they had found more than 600 suspected fake female voting cards at the home of a candidate's relative in the district of Niazyan.
And authorities said they seized thousands of fake voter cards in Kabul and the provinces of Ghazni and Ghor, reports news agency AP.
More than 2,500 candidates are standing for 249 seats in the lower house of parliament, the Wolesi Jirga.
Sixty-eight seats are reserved for women, who have been subjected to intense intimidation by the Taliban and other candidates, say human rights groups.
Up to 300,000 Afghan soldiers and police will guard the poll, backed up by nearly 150,000 foreign troops.
Preliminary results are to be announced on 22 September, with the final results due on 31 October.
There are more than 10 million registered voters, but the UN says a turnout of five to seven million would be a success, given the difficulty of holding a poll in the middle of a war.