Armed men have shot dead a candidate in next month's elections in southern Afghanistan, while an attack on the US military has wounded three soldiers near the capital.

In the latest attack directly linked to the polls, armed men on Sunday ambushed parliamentary candidate Adiq Ullah as he was driving in Uruzgan province, killing him and wounding two others in his vehicle, said provincial governor Jan Mohammed Khan.

He blamed the Taliban for the murder. Security forces pursued the attackers, but they escaped, the governor said.

Ullah's killing brings to four the number of candidates killed in the lead-up to the polls. Four election workers have also been killed and several election offices have been rocketed.

Also on Friday, armed group attacked the US service members as they were patrolling about 40km east of Kabul, a US military statement said. An attack helicopter rushed to the site, but the assailants had fled.

The statement also said that the wounded were in stable condition after being evacuated to Bagram, the main US base in Afghanistan.

Attacks on the US military so close to Kabul are rare, and Friday's assault occurred less than a week after a roadside bomb in the capital blew up near a convoy of US embassy vehicles, wounding two American staff members.

PHOTO CAPTION

Taliban militiamen. (AFP)