President Barack Obama apologized for the burning of Korans on a U.S. air base in Afghanistan as Afghans and NATO troops died in a third day of riots over the treatment of the Islamic scripture.

At least five deaths raised the riots’ Afghan death toll to 12, according to provincial officials reached by phone from Kabul. An Afghan in an army uniform killed two soldiers of the U.S.-led coalition force in Afghanistan, a statement from its headquarters said.

Obama wrote to Afghan President Hamid Karzai that “I wish to express my deep regret for the reported incident” in which personnel at the Bagram air base threw copies of the Koran and other books into a burning rubbish pile. “I extend to you and the Afghan people my sincere apologies,” Obama wrote, according to a statement from Karzai’s office.

“We will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible,” Obama said in a letter delivered by U.S. Ambassador Ryan Crocker.

Taliban leaders called on Afghans to ignore the apologies and step up attacks against Americans.

“The Muslim Afghan nation must not be deceived by their superficial apologies and must continue seeking revenge,” the Taliban leadership said in a statement e-mailed by Zabihullah Mujahid, a spokesman.

An Afghan in an army uniform shot two U.S. soldiers as hundreds of protesters were besieging their base in the eastern province of Nangarhar, said Ahmed Zia Abdulzai, the provincial government spokesman. It wasn’t clear whether the soldiers shot in that incident were the two NATO troops killed because NATO’s International Security Assistance Force, or ISAF, said in a statement that its policy prevented it from releasing the nationality of its casualties.

The U.S. embassy continued to restrict movements of its staff because of the risk of attack by Afghans angered at what protesters say was a desecration of the Muslim holy book.

Protests or riots were reported across the country. Local officials confirmed the deaths of two people in Nangarhar, two in the central province of Uruzgan, and one in the north, in Baghlan province.

Obama Apologizes for Koran Burning as Afghans, Troops Are Killed in Riots