The top United States general in Afghanistan, Scott Miller, was also at the meeting, but was not harmed, a spokesman for the US-led mission said.
It wasn't immediately clear how many North Atlantic Treaty Organisation troops were wounded.
The gunman, reported to be a security guard, opened fire as officials left a meeting in Kandahar province.
Afghan TV reported that members of the Kandahar province governor's elite guards began firing on Americans and Afghan officials during the meeting, which included Gen. Scott Miller, the head of USA and North Atlantic Treaty Organisation forces in Afghanistan.
The Taliban said General Abdul Raziq, the powerful police chief of the province with a fierce reputation for brutality, was the target of the shooting.
The blast also wounded seven people, said Omar Zwak, a spokesperson for the provincial governor.
Miller was in Kandahar on Thursday but was not wounded in the incident.
Taliban, which boycotts the elections, has carried out several attacks killing more than 30 people, including at least 10 candidates. "Initial reports also say the attacker is dead", said Col. Knut Peters, a Resolute Support mission spokesman, in an email to NPR.
He rose through the police ranks after the US -led invasion of 2001 that ousted the Taliban, serving for a time as commander of the protection force along Kandahar province's sensitive southern border with Pakistan. "We are being told the area is secure".
Three Americans, including a soldier, civilian and contractor, were wounded in the cross-fire and had been evacuated from the scene. Gen. Harold J. Greene was killed and about a dozen US soldiers were wounded when an Afghan soldier opened fire inside a building in Kabul.
He was accused of abuses, including torturing Taliban inmates, but had brought reasonable security in Kandahar, the birthplace of the Taliban militants. His forces received Western training and funds, and USA military officials often consulted him.
Earlier Wednesday, a parliamentary candidate in southern Helmand province was killed when a bomb exploded while he was holding a meeting in the courtyard of his campaign headquarters in the provincial capital, Lashkar Gah.
A bomb placed under a sofa killed four Afghans including an election candidate on Wednesday, officials said, as deadly violence escalates ahead of the October 20 parliamentary ballot.