The Taliban has claimed responsibility for a car bombing at a NATO air base in Afghanistan on Monday morning.

Nine people were killed in the suicide attack at the Jalalabad airport, which doubles as a coalition military base, as revenge for the U.S. troops burning Qurans last week. Six of those killed were Afghan citizens and the other three were airport guards. More than two dozen people were injured in the attack, including four American soldiers.

“This was carried out by one of our mujaheddin, Mawlavi Ahmadullah, who volunteered to do it in order to avenge the desecration of the Quran by the U.S. military,” Zabihullah Mujahid, a Taliban spokesman, told The Washington Post.

President Barack Obama has apologized for the Quran burning and Afghan President Hamid Karzai has urged calm, but hasn't quelled a wave of protests and violence across the country. More than 30 people have been killed since Tuesday.

We deeply regret the incident that has led to these protests. We are condemning it in the strongest possible terms, said U.S. Secretary of State Hillary Clinton, but we also believe that the violence must stop and the hard work of trying to build a more peaceful, prosperous, secure Afghanistan must continue.

In response to the violence, the United Nations evacuated its office in the northern Afghanistan province of Kunduz. Crowds of protestors attacked the U.N. office and other Afghan government buildings on Saturday. Three demonstrators were killed and 50 were injured during the protests, according to the Associated Press.

In Kabul on Saturday, a 25-year-old Afghan police officer murdered two American officers. The two were found inside the Interior Ministry with shots in the backs of their heads, according to reports.

NATO has pulled its personnel from government ministries.