A car exploded in a southern Afghan town today, killing its three occupants and a passerby, in what appeared to be a bungled suicide attack, a provincial official said.
Security has been stepped up across Afghanistan in the run-up to Sept 18 elections that have been denounced by Taliban insurgents, who have been battling US and government forces since their ouster in 2001.
The car was passing a policeman's house in the town of Girishk when it exploded but that was not believed to have been the target, said Mohammed Wali Alizai, spokesman for the Helmand provincial governor.
"It seems their aim was to carry out a suicide on attack on the Americans but it went off early," Alizai said.
"The car was completely destroyed, it's in pieces," he said.
The United States has 20,000 troops in Afghanistan, most of whom are focussing on election security, as are 10,000 NATO-led peacekeepers and tens of thousands of government forces.
More than 1,000 people, most of them insurgents but including 49 American soldiers, have been killed this year, the bloodiest period since US-led forces arrived.
The parliamentary and provincial elections are the final part of a plan meant to restore democratic government and stability in Afghanistan after 25 years of conflict.