At least two women working to register voters for Afghan elections were killed along with a child and 12 poll workers wounded when a bomb destroyed their bus in Afghanistan.
The attack in the eastern city of Jalalabad was one of the worst on workers preparing for elections supposed to be held in September, which the Taliban and allied Islamic militants have vowed to disrupt.
The Taliban quickly claimed responsibility for the attack, which was a further setback for President Hamid Karzai's efforts to bring peace to a country US President George W. Bush has described as a role model for Iraq.
"We did this because we warned people not to get involved in the election process," Taliban spokesman Abdul Latif Hakimi said. "This only strengthens the foundations of the American-backed government." He said they had also killed two US Marines in an ambush in the eastern province of Kunar on Thursday night, but had released a Turk kidnapped in March while working on a reconstruction project, partly because he was a Muslim.
The bus was heading for a registration site on the outskirts of Jalalabad when the blast occurred outside a military base on the road to the city's airport, a base for US troops.
About 4.5 million of the nearly 10 million eligible voters have registered, but the process has been slow in southern and eastern provinces, where militants are most active.
Women's registration has also lagged, especially in the south and east, partly due to difficulties recruiting female workers.
The attack was just the latest on the voter registration process and an upsurge in militant violence in the run-up to the polls has raised doubts as to whether they can be held on time.
The 20,000-strong US-led force pursuing Taliban and al Qaeda militants has warned of more attacks ahead of the polls.
The force's spokesman, Lieutenant-Colonel Tucker Mansager, told reporters that today's attack was a sign of the militants' desperation and they would not succeed in derailing the polls.
Until Saturday, at least 33 foreign and Afghan humanitarian workers had been killed in 18 months, severely disrupting aid and reconstruction work, as well as hampering election preparations.