The Taliban on Monday vowed to target Afghanistan's presidential election, urging their fighters to attack polling staff, voters and security forces before the April 5 vote to choose a successor to Hamid Karzai.
Previous Afghan elections have been badly marred by violence, with at least 31 civilians and 26 soldiers and police killed on polling day alone in 2009 as the Islamist militants displayed their opposition to the US-backed polls.
Another blood-stained election would damage claims by international donors that the expensive military and civilian intervention in Afghanistan since 2001 has made progress in establishing a functioning state system.
NATO combat troops are withdrawing from the country after 13 years of fighting a fierce Islamist insurgency that erupted when the Taliban were ousted from power after the 9/11 attacks on the United States.
"We have given orders to all our mujahideen to use all force at their disposal to disrupt these upcoming sham elections -- to target all workers, activists, callers, security apparatus and offices," the Taliban said in an emailed statement.
"It is the religious obligation of every Afghan to fulfil their duty by foiling the latest plot of the invaders that is guised in the garb of elections."
Billions of dollars have been spent on military operations and development in Afghanistan, but the country remains wracked by poverty and violence with weak government structures and a fragile economy dependent on aid money.
The next president will face a testing new era as the Afghan army and police fight the Taliban without NATO assistance and as international funding declines.
Efforts to open peace talks with the Taliban have so far failed, but negotiations are likely to be given another push by the incoming government as it tries to bring stability to areas in the south and east where the militants hold sway.
The Taliban have targeted every election since the 2004 poll, but the statement on Monday was the first explicit threat from the militants against this year's vote.
Among the front-runners are Abdullah Abdullah, who came second in 2009, former foreign minister Zalmai Rassoul and former World Bank economist Ashraf Ghani.
The campaign has been relatively peaceful so far, though gunmen shot dead two of Abdullah's aides in the western city of Herat.
"We once again call on all of our countrymen to keep away from electoral offices, voting booths, rallies and campaigns so that may Allah forbid, their lives are not put into danger," the Taliban said.
"If anyone still persists in participating then they are solely responsible for any loss in the future."
The statement added that "the actual election has already taken place in the offices of the CIA and Pentagon and their favourite candidate has already won", without mentioning any candidate by name.
The Afghan government did not immediately respond to the Taliban threat, but officials have said that almost all polling centres will be safe enough to open and that the security forces are on alert to ensure a peaceful election.
All remaining 55,000 NATO combat troops will leave Afghanistan by December, but a small US force may be deployed from 2015 on counter-terrorism and training operations if the next president signs a security deal with Washington.
Karzai negotiated the deal but then refused to sign it in a move that plunged Afghan-US relations to a new low.
Election campaigning slowed on Monday as Afghanistan started three days of official mourning for Vice President Marshal Mohammad Qasim Fahim, who died on Sunday.