Afghan police at least six people have been killed in a suicide car bombing at the gates of Jalalabad airport in eastern Afghanistan.

Several others were wounded in the blast early Monday. Provincial officials say most of the casualties appear to be civilians.

The Taliban has claimed responsibility for the attack.

It was not immediately clear if the attack was related to days of unrest across Afghanistan following the burning of Qurans by NATO personnel at Bagram Air Base. More than 30 people, including four U.S. military personnel, have died in protests since the Quran burning.

On Sunday, Afghan authorities began an intense search for an Afghan intelligence official suspected of killing two U.S. officers Saturday inside a command center at the Interior Ministry in Kabul.

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

Afghan President Hamid Karzai addressed the shooting Sunday in Kabul and called for calm. Mr. Karzai said he is sorry for those who were killed and extends his condolences to their families.

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

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 Afghan Taliban has claimed responsibility for the incident at the Interior Ministry, saying the attack was retaliation for the burning of the Quran.