Afghan officials and witnesses say NATO soldiers were handing out gifts to children Monday when a suicide bomber on a bicycle struck the gathering in Kandahar province's Panjawi district.
The bombing came a day after the NATO-led International Security Assistance Force and Afghan forces jointly declared the district free of Taleban insurgents.
A spokesman for the international force, or ISAF, Luke Knittig, says Monday's bombing wounded a number of people, including civilians.
"I can confirm that four ISAF Soldiers have been killed and a number of soldiers and civilians injured, some seriously," he said. "Our operations there continue. But obviously our immediate focus is on evacuating these soldiers for treatment and responding to the incident."
Knittig provided little information and did not disclose nationalities of the slain soldiers. Afghan officials have been quoted as saying the suicide bomber targeted Canadian troops.
A purported Taleban spokesman speaking to local Afghan reporters by telephone Monday claimed responsibility for the attack.
On Sunday, the commander of the NATO forces in Afghanistan declared at a news conference that a joint offensive with Afghan troops had forced Taleban insurgents from the districts of Zhari and Panjawi, the scene of Monday's suicide bombing.
The anti-insurgent offensive lasted for two weeks. NATO says nearly 500 Taleban militants were killed, but the extremist Islamic group denied suffering such heavy losses. Five Canadian soldiers were also killed during the operation, and 14 British troops died when their aircraft crashed.