NATO and Afghan officials say a suicide bomber blew himself up near foreign troops in the southern province of Kandahar, killing three people.
Afghan authorities say three civilians were killed when the bomber detonated explosives as troops patrolled a busy street on foot Thursday in Maiwand district.
NATO confirms that three people were killed in what it describes as a suicide car bombing in Maiwand, but it says two soldiers and one civilian died. It says 21 Afghans were wounded.
The Taliban has claimed responsibility for the attack.
Earlier, Afghan President Hamid Karzai expressed concern about reports that 17 civilians, including women and children, were killed in a U.S.-led military operation this week.
The U.S. military said only militants were killed in the operation Tuesday in Laghman province.
A statement from President Karzai's office Thursday demanded that coalition troops stop endangering civilians in their fight against insurgents. It also condemned the militants for using civilians as human shields.
President Karzai did not identify the source of the reports of civilian casualties.
U.S. military spokesman Colonel Jerry O'Hara said Thursday that the U.S. would consider any new information about the incident.
Australia's Defense Force confirmed Thursday that it, too, is investigating claims that civilians were wounded or killed in a separate battle between Taliban insurgents and NATO forces in Uruzgan province earlier this week.
Afghanistan's Interior Ministry said 11 civilians died in that fighting.
Some information for this report was provided by AFP, AP and Reuters.