Eric Lach April 4, 2011, 9:54 AM

After a weekend of deadly riots in Afghanistan, Gen. David Petraeus issued a statement on Sunday publicly condemning the Quran burning that sparked the unrest. And in an interview with the Wall Street Journal, the commander of U.S. and NATO forces in the country admitted that the burning has created an “additional serious security challenge.”

Seven U.N. workers and four Afghans were killed in Mazar-i-Sharif on Friday, when a demonstration against the burning of a Quran by American pastors turned violent. The Associated Press reports that at least nine more people were killed in protests in Kandahar on Saturday, and two more deaths were reported there on Sunday. Sunday protests in Jalalabad were described by the AP as “largely” peaceful.

On March 20, fringe pastor Terry Jones oversaw the “trial” and burning of a Quran at his tiny church in Gainesville, Florida. While Jones’ threat to burn Qurans on 9/11 last year drew much media attention, the March event went largely unnoticed. But on March 24, Afghan President Hamid Karzai called on the United States to bring those responsible to justice — bringing the issue to the attention of many Afghans, according to the WSJ. On Friday, thousands of people gathered at a mosque in Mazar-i-Sharif, where “[s]peaker after speaker denounced the Quran-burning.” Afterward, the crowd marched to the nearby U.N. compound.

Petraeus and NATO Ambassador Mark Sedwill issued a statement Sunday condemning the Quran burning, and emphasizing that it was the action of a small number of “extremely disrespectful” people.

“In view of the events of recent days, we feel it is important on behalf of ISAF and NATO members in Afghanistan to reiterate our condemnation of any disrespect to the Holy Qur’an and the Muslim faith,” the statement said. “We condemn, in particular, the action of an individual in the United States who recently burned the Holy Qur’an.”

Petraeus, who met with Karzai on Sunday, told the WSJ the issue poses new challenges.

“Every security force leader’s worst nightmare is being confronted by essentially a mob, if you will, especially one that can be influenced by individuals that want to incite violence, who want to try to hijack passions, in this case, perhaps understandable passions,” he said. “Obviously it’s an additional serious security challenge in a country that faces considerable security challenges.”

On Saturday, President Obama issued a statement denouncing the Quran burning as “an act of extreme intolerance and bigotry,” while also condemning the acts of violence in Afghanistan.

Meanwhile, Jones reported receiving death threats. The pastor, who took no responsibility for the violence and even said that “in the long run, we may save hundreds or thousands,” told ABC News he has received over 300 threats.

Watch Petraeus and Sedwill speak about the situation:

Afghanistan, David Petraeus, Terry Jones