The insurgents have threatened to target polling stations tomorrow when voters will choose between ex-foreign minister Abdullah Abdullah and ex-World Bank economist Ashraf Ghani.
The second-round vote tomorrow comes as US-led NATO troops withdraw after more than a decade of fighting the Taliban, who were ousted from power in 2001 for sheltering Al-Qaeda militants behind the 9/11 attacks.
Afghan officials are desperate to repeat the success of the first-round vote in April, when the insurgents failed to launch a single high-profile attack as long lines of voters turned up across the country to cast their ballots.
"We have very good planning and coordination with our security forces, and they are on the highest state of alert... The enemy suffered a heavy blow last time, so they have vowed to disrupt the run-off."
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Outgoing President Hamid Karzai has also ordered security personnel to remain neutral in tomorrow's poll, as officials try to avoid the massive fraud that undermined the 2009 poll when he retained power.
Abdullah secured 45 per cent of the first-round vote, with Ghani on 31.6 per cent, according to the final results, which came after weeks of deliberation over fraud allegations.
General Mohammad Zahir Azimi, the ministry of defence spokesman, said about 400,000 soldiers, police and intelligence forces were involved in the poll security plan.
The Taliban in a statement warned Afghans to "remain far away from the polling stations... Lest you should be hurt or killed.