As more U.S. troops head for Afghanistan, the military situation there will "get worse before it gets better," Gen. David Petraeus said Tuesday.

His remarks, made at a forum at the John F. Kennedy School of Government, echoed warnings he made before the 2007 "surge" of U.S. troops credited in part with eventually calming violence in Iraq.

Petraeus, who heads U.S. Central Command and oversees the wars in Iraq and Afghanistan, cited the revived Taliban and the rise in drug trafficking, which supports militants.

"We are going to make progress, but it’s going to get worse before it gets better," The Associated Press quoted Petraeus as saying. "When you go into an enemy’s territory ... they are going to fight you for it."

President Barack Obama has ordered that the U.S. military double its current commitment of 38,000 troops in Afghanistan. The number of troops in Iraq could fall to between 30,000 and 50,000 by the end of 2011.

The troop increase in Afghanistan must be accompanied by an understanding of the cultural differences between Afghanistan and Iraq, but with a similar approach of establishing a presence out in the communities, Petraeus said.

"You can’t commute to the fight," said Petraeus, summarizing the philosophy he also applied in Iraq. "You can’t clear and leave. You have to clear and hold, and then build."

He said Americans will need to reach out to moderate elements of the Taliban.

"The question is how to do that," he said, according to The Boston Globe. "You have to do that certainly at local levels. You have to find out who are the really hard-core folks and get them out of there."

But he also warned of the risks of building up provincial governments, which could pose a challenge to the Afghan national government.

Petraeus characterized the mission in Afghanistan as being more straightforward than the one in Iraq.

"I think we know why we went to Afghanistan," he said. "There is actually no debate about where the 9/11 attackers came from. The strategy has to be to keep conditions from returning to those that allowed al-Qaida and transnational extremists from finding sanctuaries."

Petraeus also said the leaders of Pakistan should recognize their biggest threat comes from Islamic extremists within its borders, and not from India.

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