"Along with other international donors, we have called repeatedly for the Afghan government and electoral institutions to make preparations for a credible and transparent presidential election.
Afghan voters who risk their lives to participate in elections deserve to know the outcome accurately reflects the voters' choice," TOLO News quoted the State Department as saying on a statement on Wedmesday
"Coalition forces and donors who have sacrificed to give Afghans the ability to choose their leaders deserve to have this confidence as well."
The statement also called on the Taliban to not disrupt the process and to refrain from violence.
"We call on all parties, including the Taliban, to ensure Afghan voters can go to polling centres on election day without fear of intimidation, attack, or violence. We strongly condemn the threats made by the Taliban against election workers and voters.
"Any attempt to intimidate, coerce, or buy voters is an attack on democracy. We offer our strong support to the Afghan National Security Forces, who day-in and day-out sacrifice their lives for the cause of peace and stability," it added.
The September 28 election will be the fourth presidential election in Afghanistan since 2001, when US troops invaded the country to oust the Taliban regime.
A total of 18 contenders are in the fray including sitting President Mohammad Ashraf Ghani and his Chief Executive Abdullah Abdullah.
More than 9 million eligible voters are expected to cast their ballots.
The Afghan National Defence and Security Forces (ANDSF) have beefed up security operations against Taliban fighters as the militants have launched massive attacks on cities and districts across the country.
( With inputs from IANS )