Pakistani military sources told American ABC television that five of those killed were "high level Al-Qaeda figures", and their bodies are undergoing forensic tests for identification.
They said Zawahiri, who is considered Al-Qaeda's second most senior figure after Osama bin Laden, may have been one of the victims. Zawahiri has been known to stay at houses in the village of Mamud, in the tribal zones of eastern Pakistan.
NBC television cited US defence sources who said the strike targeted Zawahiri, who has been indicted in the United States for his role in 1998 attacks on US embassies in Africa.
Residents in the village reported the attack earlier, and said 18 people were killed. But the US Defence Department has denied the US military carried out any attacks in the area.
"There is no reason to believe the US military is conducting operations there," said Lieutenant Colonel Todd Vician.
But the CIA is also known to conduct operations along the Pakistan- Afghanistan border in the hunt for bin Laden and his deputies. A medical doctor, Zawahiri has become Al-Qaeda's most senior spokesman in videos released in recent months, with bin Laden keeping a low profile.
He appeared in a new video released last week, leading some to believe that he has become the group's effective leader.
At least 18 people, including women and children, died as missiles struck the village of Mamund in Pakistan's northeastern Bajur tribal region bordering Afghanistan, residents said earlier.
Villagers said the missiles destroyed three houses, leaving five women, five children and eight men dead. Pakistan has deployed around 70,000 soldiers into the tribal areas in efforts to flush out Al-Qaeda and Taliban fighters who fled Afghanistan after the US-led invasion in late 2001, who are believed to be hiding out in the region. The US placed a US$25 million bounty for Zawahiri after the September 11, 2001 attacks on New York and Washington