The top U.S. commander in Afghanistan on Sunday condemned the burning of a Quran in the United States, days after demonstrators retaliated by killing workers for the United Nations and protests in cities around the country have escalated into violence.

U. S. Gen. David Petraeus, who is leading attacks against insurgents in Afghanistan said the March 20 act of burning Islam's holy book by a Florida pastor was hateful, it was intolerant and it was extremely disrespectful and again, we condemn it in the strongest manner possible.

Protesters and police clashed in the city of Kandahar on Sunday. One police officer was shot dead, two other officers were injured, and 18 civilians were wounded, provincial health director Qayum Pokhla told the Associated Press.

Hundreds of people blocked the main highway in Jalalabad, shouting for U.S. troops to leave, burning an effigy of President Barack Obama and stomping on a U.S. flag, according to the report.

On Saturday, President Barack Obama sent condolences to the families of those killed.

The desecration of any holy text, including the Koran, is an act of extreme intolerance and bigotry, Obama said.

However, to attack and kill innocent people in response is outrageous, and an affront to human decency and dignity.

He called on people to draw upon the common humanity that we share.

Seven United Nations Workers and four demonstrators were killed on Friday in the city of Mazar-e-Sharif after mosque preachers strongly protested and attacked the burning, according to the Los Angeles Times.

On March 20, Florida Pastor Terry Jones, who last year put off a burning of the Koran, allowed for the book to be burned by one of his assistants at his Doveworld Outreach compound in Gainsville, Florida at an event resembling a trial.