Afghan officials say a suicide bomber killed at least 40 people late Wednesday and wounded more than 70, including children, at a wedding party in Kandahar's Arghandab district.
Guests at the wedding described seeing a huge fireball at the time of the explosion.
Video taken after the explosion showed blood covered victims -- some of them children -- wrapped in bandages at a local hospital while survivors gathered around the rows of coffins outside a hospital morgue.
Officials say the groom and others were targeted because they had links to a local anti-Taliban militia.
On Thursday, the deputy commander of NATO forces in Afghanistan, Lieutenant General Nick Parker, placed the blame on Taliban militants. He said the ruthless violence demonstrated "the Taliban's sickening and indiscriminate tactics" and proved the Taliban have no regard for human life.
But a Taliban spokesman, Yousuf Ahmadi, denied responsibility and blamed foreign forces for the attack. The militant group often denies causing civilian casualties.
Afghan President Hamid Karzai also condemned the attack, calling it a crime against Islam and humanity.
The U.S. embassy in Kabul offered condolences and said the United States stands with the Afghan people against the "scourge of terrorism." The attack on the wedding is just the latest in a series of militant attacks in recent days.
Eighteen NATO troops have been killed since Monday, including four who died Wednesday after the Taliban shot down their helicopter in neighboring Helmand province.
U.S. Defense Secretary Robert Gates has warned of a "very tough summer" of violence as U.S. forces push deeper into Kandahar. But he also says that he expects enough progress will be made to justify a continued presence in the country.
Some information for this report was provided by AP, AFP and Reuters.