Campaign worker Esmatullah, who like many Afghan men uses only one name, was returning home from visiting a friend on Monday afternoon when unknown gunmen opened fire outside his house in Logar province, provincial spokesman Din Mohammad Darwish said.
Esmatullah — known as Commandor Tor for his role in the struggle against the 1990s Soviet occupation — was killed instantly while his two bodyguards were wounded, Darwish said
Esmatullah worked as an election observer for presidential candidate Abdul Rab Rassoul Sayyaf, a prominent Islamic cleric who is currently running fourth in the race for the top post, according to the partial results that have been released.
A spokesman for Sayyaf's campaign, Mohammad Fahim Kadamani, confirmed that Esmatullah was an election observer and blamed the Taliban for his death.
But the Taliban spokesman, Zabiullah Mujahid, denied involvement. He told The Associated Press by telephone on Tuesday that the insurgents would not target Esmatullah because of his high status as a former mujahedeen fighter against the Soviets.
"We respect him. He was a good man," Mujahid said.
The Taliban have unleashed a wave of attacks during the election to replace President Hamid Karzai, who under Afghan law cannot serve a third term.
Candidates, campaign workers and government offices have all been targeted with bombings and armed attacks, although the insurgents failed to disrupt election day itself, which saw some 7 milllion Afghans turn out to cast votes.
Preliminary results of the vote are due on Thursday, though it is likely that a second round — a runoff between former foreign minister Abdullah Abdullah and ex-finance minister Ashraf Ghani Ahmadzai — will be necessary, dragging out the entire election process until at least June.
Abdullah is leading with 44.4 per cent of the partial results and Ahmadzai is in second place with 33.2 per cent. If neither candidate gains a majority of the vote, a runoff is required under electoral law.