Several guerrillas opened fire with assault rifles on the workers' car in the village of Malang Karez in Kandahar's Maiwand district, district chief Khan Agha told Reuters, adding that the man killed was the driver of the car.
The U.N. official said the men were employees of the U.N.-Afghan commission, known as the Joint Electoral Management Body (JEMB), which is organising parliamentary elections due to be held on Sept. 18.
Taliban spokesman Abdul Latif Hakimi phoned Reuters to claim responsibility for the attack.
A surge in militant violence in recent months, in which hundreds of people have died, has raised concerns about security for the polls.
The worker was only second to be killed in the run up to the election.
Another, from an Afghan non-governmental group involved in educating the public about the vote, was shot dead in early June in troubled Uruzgan province, which is a neighbour of Kandahar.
The election is the next big step in Afghanistan's difficult path to stability.
The United Nations helped organise a presidential election last October. Several election workers were killed in the run-up to that vote but election day was largely peaceful and turnout was high.
However the parliamentary poll will be far more complex and will require a big security operation, not only to prevent rebel violence but also to stop intimidation by regional strongmen vying for power after three decades of conflict.
In all, 2,884 people, 342 of them women, have signed up to run for the 249-seat lower house of parliament, known as the Wolesi Jirga.
- Reuters - Thomson Reuters Foundation
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