But the Taliban said the assailant was 28 and from Logar Province. “Conducting such a successful attack on an important C.I.A. center in Kabul City is something that a 12-year-old boy is not able to do,” said Zabiullah Mujahid, a Taliban spokesman.

The attack came a day after the United States designated a Taliban affiliate, the Haqqani network, as a terrorist group. The Haqqanis have carried out attacks in Kabul.

A NATO official in Kabul said the coalition did not yet know whether the Haqqanis were responsible. “I don’t think you can link the two,” the official said, referring also to the terrorist designation. He asked not to be identified because the investigation was still under way. But a spokesman for the Ministry of Interior, Siddiq Siddiqi, said in a Twitter message that he thought the Haqqanis were behind the attack.

Even as the bomber struck Kabul, former warlords who fought the Soviets and the Taliban in the 1980s and 1990s gathered to commemorate the 11th anniversary of the death of the former mujahedeen commander Ahmed Shah Massoud, who is considered a national hero by many here.

At a time when the American-led coalition is trying to oversee a peaceful transition to full Afghan control, the warlords, including some in the government, joined a meeting of about 1,000 officials in Kabul to urge former mujahedeen fighters to take up arms against the Taliban.

“If the Afghan security forces are not able to wage this war then call upon the mujahedeen,” said Marshal Muhammad Qasim Fahim, the first vice president.

Another former warlord who addressed the meeting, Abdul Rab Rassoul Sayyaf, said the government no longer inspired respect and fear, and urged officials to be tougher. “You can’t achieve peace and security through pleading and begging,” he said.