Hamid Karzai, the Afghan president, has called Wednesday's attack against a wedding party in Kandahar "a crime of massive inhuman proportions."
The Taliban denied carrying out the attack, which killed more than 40 people and wounded dozens more, including the groom.
Karzai spoke at a news conference with David Cameron, the British prime minister, who made his first official visit to Afghanistan on Thursday. Cameron joined Karzai in condemning the attack.
Despite the Taliban's denial, local authorities suspect the group was responsible: Many of the guests at the wedding party have links to local defence programmes which co-operate with Western forces.
More money, no new troops
Cameron announced increased aid for Afghanistan, and declared it Britain's "most important foreign policy issue," but also ruled out sending extra troops.
He said Britain would spend an additional $98 million to counter the threat of roadside bombs and provide additional aid funding for Afghanistan to build up its army, police and civil service capacity.
"I've described this year - and the president, I know, agrees - in terms of the Nato mission in Afghanistan as the vital year," Cameron said.
"What we want, and is our national security interest, is to hand over to an Afghanistan that is able to take control of its own security."
But Cameron said that "the issue of more troops is not remotely on the UK agenda". Britain currently has 9,500 troops in Afghanistan as part of a 46-nation force led by the US.
James Bays, Al Jazeera's correspondent in Kabul, said Cameron appeared on the surface to be going along with US policy but could reconsider the British position in coming months.
"We didn't really hear any great change of policy ... but I think there might be a little bit of a change of thinking behind the scenes," he said.
"People who know him well have told me that he is open minded and if he believes that the [US] McChrystal plan is not working and Britain's national-security interests are not best served in Afghanistan, then he will reconsider the situation in the coming months."
Barack Obama, the US president, has given General Stanley McChrystal, the commander of US and Nato forces, until the end of the year to assess whether his troop "surge" in the country is working and when they can start drawing down forces.
Cameron's government has said it will give McChrystal strategy in Afghanistan time to work, but British officials are looking at what could be done more effectively.
Rising casualties - nearly 300 British soldiers have been killed in Afghanistan since 2001 - are eroding public support for the war in the UK, while its cost is straining already stretched public finances.
"No one wants British troops that stay in Afghanistan for a day longer than is necessary," Cameron said.