BAGRAM AIR BASE, Afghanistan—Afghan tribes are needed as crucial battlefield allies against the Taliban and other extremists in the same way local militias rose up to oppose insurgents in Iraq, the new military overseer of America’s two wars said Thursday.

The tactic has long been endorsed by Gen. David Petraeus—the former top U.S. commander in Iraq whose outreach to Sunni sheiks helped oust al-Qaida-inspired militants from key areas and sharply decreased attacks.

But his latest comments—on his first trip to Afghanistan since taking charge of U.S. Central Command last week—appeared aimed at pressing the Afghan leadership to recognize the need for tribal militia allies at a time when violence in Afghanistan is at its highest levels since 2001.

It also reflects Washington’s expected shift in military focus from Iraq to Afghanistan and the neighboring tribal areas in Pakistan, which President-elect Barack Obama has described as the main showdown against the resurgent al-Qaida, Taliban and other militants.

“This is a country in which support of the tribes, of the local communities, for the overall effort is essential,” Petraeus told The Associated Press at the massive Bagram Air Base north of Kabul. “It is a country that has not have a tradition of central government extending into the far reaches of its provinces and its districts.”

Petraeus declined to discuss details of efforts—spearheaded publicly by President Hamid Karzai’s government—to bring Afghan militiamen into the battle alongside Afghan forces, U.S. soldiers and other NATO-led troops.

Yet Afghanistan poses even more potential complications than the so-called Awakening Council movement in Iraq.

More than 150 major tribes range across the eastern and southern border lands with Pakistan—where the majority of the extremist attacks occur—and any military alliances with selected groups risk stirring rivalries and internal power struggles in regions outside central government control.

The tribes in the areas are almost exclusively Pashtun, the majority group in Afghanistan. Perceptions of special favors to already powerful Pashtun tribes—including pay and possible weapons supplies—could bring backlash from other ethnic groups with their own militiamen and warlords that clashed in brutal civil wars in the 1990s.

In Iraq, the equation was different: the Awakening groups came mostly from the minority Sunnis who lost their privileged status with Saddam Hussein’s fall. Now, the Shiite-led Iraqi government is under pressure from Washington to incorporate the militias into the security forces.

The Pentagon did not provide weapons directly to Awakening allies in Iraq. But Petraeus left open the possibility that Karzai could offer arms in exchange for tribal alliances.

“We will certainly support what President Karzai decides to adopt,” said Petraeus. “We traditionally have not armed tribes ... But again, we have to see how that evolves here and see what kinds of initiatives and structures might be looked at.”

Across the border in Pakistan, the government in Islamabad has already started arming tribal militias for roles as front line forces against al-Qaida and Taliban safe havens.

And—like in Iraq—the payback from extremists can be deadly. Dozens of government-allied tribesmen have been killed in recent attacks in Pakistan.

The message is clear to any Afghan tribal leader weighing offers to join Kabul’s fight.