(CNN) -- The top U.S. general, David Petraeus, painted a bleak picture of Afghanistan's immediate future, saying insurgent attacks have risen to record levels not seen since 2001.

U.S. General David Petraeus chats with John Nagl, president of Center for a New American Security.

"There is no question that the situation has deteriorated over the course of the past two years and that there are difficult times ahead," said Gen. David Petraeus, who heads the US Central Command, on Thursday.

"The past week was the highest level of security incidents in Afghanistan's history, at least that post-liberation history," Petraeus said in a speech at the annual conference of the Center for a New American Security, a Washington think tank.

Petraeus's comments came as the United States is embarking on new strategy in Afghanistan, with increased troop levels and a focus on counterinsurgency tactics. Petraeus said America should draw on the lessons learned in Iraq.

At the height of Iraq's insurgency, it suffered 160 violent attacks a day, he said. That number has failen to between 10 and 15 a day.

Petraeus masterminded the so-called surge strategy, which is credited with helping stabilize Iraq.

Iraq continues to move forward, but Afghanistan "is headed in the other direction," Petraeus said.

He said some of the violence "will go up because we are going to go after their sanctuaries and their safe havens as we must."

Afghanistan posed unique challenges, Petraeus said, adding that it was imperative for U.S. soldiers to live near local people, build relationships and have a "phenomenal understanding" of the local culture. He said training fledgling Afghan security forces will be critical to long-term success, just as it was in Iraq. Watch some Afghans express optimism about the country's prospects »

President Barack Obama has approved a plan that increases U.S. presence by 21,000 troops. Last month Defense Secretary Robert Gates injected fresh energy into the beleaguered war effort by tapping Lt. Gen. Stanley McChrystal, a former special operations chief, to take over as the top U.S. commander in Afghanistan.

In May, Obama met with Afghanistan and Pakistan's presidents and pledged a more coordinated effort to defeat the insurgents. He has called for improved troop training and added civilian expertise in an effort to battle a resurgent Taliban.

After the September 11 terrorist attacks in 2001, the United States invaded Afghanistan and toppled the Taliban. But in recent months, the country has seen a resurgence in extremism and a rise in violence.

So far this year, 73 U.S. soldiers have died in Afghanistan, more than half of the 133 coalition deaths.

All About Afghanistan • The Taliban • Terrorism • Barack Obama