Taliban fighters have kidnapped and then killed 16 people in an Afghan province after finding them with voter registration cards for the country's September elections.
The killings on Friday night in the province of Zabul were the most serious attack yet on the elections, which the Taliban and allied Islamic militants have vowed to disrupt.
News of the violence came a day after a bomb killed two women working for the UN-Afghan electoral body and wounded nine women poll workers and two children in the eastern city of Jalalabad.
Mr Haji Obaidullah, chief of Khas Uruzgan district in the central province of Uruzgan, said the guerrillas stopped a bus carrying 17 civilians through the district on Friday.
They took the passengers to Dai Chopan district of the neighbouring province of Zabul and killed all but one when they found they were carrying voter registration cards, he quoted the lone survivor as saying.
"They were apparently killed because they were carrying the registration cards," he said.
Several hundred US and Afghan soldiers backed by air support were searching for the villagers' bodies and the attackers.
A Taliban spokesman claimed responsibility for killing the women in Jalalabad by bombing their bus. He said they had warned Afghans not to become involved in elections that would only strengthen the US-backed government.
An upsurge in militant violence in the run-up to the polls has raised doubts as to whether they can be held on time.
About 4.5 million of nearly 10 million voters eligible have registered, but the process has been slowed in the south and east by militant threats and violence. Female registration has lagged, partly because of problems recruiting female election workers.
The latest attacks are further setbacks for President Hamid Karzai's efforts to bring peace to Afghanistan, a country US President George W. Bush has described as a role model for Iraq.
Mr Karzai appealed to NATO on Friday to make good its pledge to send more troops to protect the presidential and parliamentary polls to ensure they can be held as scheduled.
At a summit in Istanbul starting tomorrow, NATO is to announce that its 6,400-strong peacekeeping force will take command of more military-civilian reconstruction teams in northern Afghanistan and deploy about 1,200 troops for the polls.
But this will fall short of the figure of at least 5,000 extra troops the government and the United Nations say are needed, and the deployments will be to relatively secure areas, not to the south and east where militants are most active. Analysts say Mr Bush, Mr Karzai's main supporter, wants a September poll so that he has a foreign policy success to balance against Iraq before his own re-election bid in November.