Nine people have been killed in a suicide car bombing outside the gates of a NATO base and the Jalalabad airport in eastern Afghanistan, acording to Afghan police.

Afghan President Hamid Karzai condemned the “inhuman and un-Islamic” attack that officials say killed six civilians, an Afghan soldier and two guards, 12 others were wounded.

A Taliban spokesman said the suicide bombing was revenge for last week's Quran burning at Bagram Air Base. More than 30 people, including four U.S. military personnel, have died in nearly a week of protests since the incident.

The unrest has continued despite apologies from U.S. President Barack Obama and appeals for calm from President Karzai.

On Sunday, a protester was killed and seven American soldiers wounded in a grenade attack at a U.S. base in northern Kunduz province.

Afghan authorities are also searching for an Afghan intelligence official suspected of killing two U.S. military advisors Saturday at the Interior Ministry in Kabul.

The American officers were found dead inside a locked office that can be accessed only by people aware of the combination to the lock.

All international military personnel working in Afghan government offices were recalled Saturday after the shooting. NATO said the decision to order the recall came “for obvious force protection reasons.”

The Taliban claimed responsibility for the incident at the Interior Ministry.

The U.S. Embassy has been in lockdown since the violence erupted and has warned of a “heightened” threat to Americans in Afghanistan.

On Sunday, the U.S. ambassador to Kabul, Ryan Crocker told CNN that tensions are running very high. “I think we need to let things calm down, return to a more normal atmosphere, and then get on with business.”

Afghan defense and interior ministers have postponed scheduled trips to the United States this week so they could remain in Afghanistan to monitor the situation.