ISLAMABAD, Pakistan  A missile believed to have been fired Thursday from an American drone killed the younger brother of a top militant commander in the North Waziristan tribal area, according to several Pakistani security and intelligence officials, residents in Waziristan and a friend of the commander’s family.

The militant commander, Sirajuddin Haqqani, appeared to have been the target of the attack. Mr. Haqqani, who the Americans say operates from a base in North Waziristan, took over major responsibilities for the family’s militant network in recent years from his father, Jalaluddin Haqqani, who has been reported to be ill. The Americans blame the Haqqani network for helping plan the suicide bombing against the C.I.A. base in Afghanistan in December in which C.I.A. operatives and a Jordanian intelligence officer were killed.

The brother, Mohammad Haqqani, was killed along with three others when their white station wagon was hit by a missile in Dande Darpakhel, a village in North Waziristan, bordering Afghanistan. Americans believe that Sirajuddin Haqqani is closely affiliated with Al Qaeda and that his network is the most potent one working against international forces in eastern and central Afghanistan.

Dande Darpakhel is just north of Miram Shah, the capital of North Waziristan, and is considered the main base of the Haqqani network and family. It has been a repeated target of missile strikes, one of which was believed to have killed several members of the clan last year.