Voice of America reported Monday that some believe the United States has carried out more than 20 missile attacks by unmanned spy planes in tribal areas since August to target militants.

The latest missile attack targeted militants in South Waziristan, near the Afghan border.

Witnesses said one of the vehicles fired shots at the drone before the missile destroyed it. VOA reported that it is not known whether any high-profile al-Qaida or Taliban leaders were killed in the strikes.

A local intelligence official told CNN those killed were suspected Taliban militants. Another official was quoted as saying nine other militants were wounded in the attacks.

Such missile attacks are usually launched by unmanned drone planes although the U.S. military in Afghanistan doesn't comment on such suspected cross-border strikes.