The men’s deaths were confirmed by Gen. Mohammed Zahir, a police official in Kabul.

The killings marked another potentially heavy blow for Mr. Karzai, coming just days after his powerful half-brother was assassinated by a close associate in southern Afghanistan.

About 90 minutes after the attack began at 8:30 p.m., Afghan security forces still had not captured or killed all of the gunmen. It was unclear whether anyone else had been killed or wounded, or whether the assailants had taken hostages.

“The terrorists are still inside, in one of the rooms,” General Zahir said. “We are trying our best.”

Hundreds of police officers, soldiers and Afghan intelligence officers swarmed the scene in one of Kabul’s more affluent neighborhoods, filling the streets where government officials and businessmen live behind high walls and steel gates, protected by many men with guns.

Sporadic gunfire rang through the dark streets, but it was unclear who was shooting.

The slaying of another Karzai ally from Afghanistan’s still-violent southern belt heightened concerns that militants were attempting to weaken the president’s standing and unravel fragile security gains there after months of intense fighting by NATO and Afghan forces.

Oruzgan sits just to the north of Kandahar Province, the Taliban heartland where Mr. Karzai’s half-brother, Ahmed Wali Karzai, had been a polarizing but powerful leader. The Taliban have claimed responsibility for killing Ahmed Karzai, but the motives of the gunmen — who was himself killed — remain unknown.

Imprisoned during the Taliban’s rule, Mr. Khan was seen as an eager and bitter foe of insurgents who worked with the NATO-led coalition during his time as governor. But he was dogged by accusations of corruption and failure to provide basic public services, lost his post in 2006 and was brought to Kabul.

A spokesman for the NATO-led International Security Assistance Force said that Afghan officials had not requested any help from coalition forces.

*Sangar Rahimi contributed reporting.