Seven protesters were killed in the western province of Herat and one in the Pul-e-Khumri district of Baghlan province, the BBC reported.
U.S. troops at the largest NATO air base in Afghanistan Monday burned several Korans in which prisoners had written messages to each other.
At least 20 people have died in protests since Monday, including two U.S. soldiers.
The Taliban Thursday released two statements in response to the Koran burnings, The New York Times reported.
One urged Afghans to attack foreign troops and installations as well as Afghan forces defending them and the other urged Afghan security forces to turn their weapons on their NATO colleagues.
"The Islamic Emirate of Afghanistan calls on all the youth present in the security apparatus of the Kabul regime to fulfill their religious and national duty," one of the statements said, "to repent for their past sins and to record their names with gold in the history books of Islam and Afghanistan by turning their guns on the foreign infidel invaders instead of their own people."
U.S. President Barack Obama issued an apology to the Afghan people Thursday, calling the incident a "genuine mistake."
In Washington, White House deputy press secretary Josh Ernest said Obama was pleased that Afghan President Hamid Karzai had appealed for calm in Afghanistan.
Obama, who has caught flak for his apology on the Republican presidential campaign trail and on the Internet in comments about his action, thought an apology was appropriate "because he's putting the best interests and safety and welfare of our service members and our civilians who are currently serving in Afghanistan right now," Ernest said Friday, "[and] that the American people, and the American military in particular, does have respect for the religious views and the religious practices of the Afghan people."
The message from Obama, Defense Secretary Leon Panetta and Gen. John Allen, commander of the coalition forces, has been one "that the United States military and indeed the American people have enduring respect for the religious views or religious practices of the Afghan people," the White House spokesman said.
Asked whether the administration was hoping for an apology from Karzai, Ernest said, what Obama his national security team and the U.S. military leadership in Afghanistan "are focused on is making sure that we accomplish our goals in Afghanistan."
"There is no doubt that we're working through a difficult situation there, but we are going to stay on track of accomplishing our goal and continuing to make the significant progress that we have made in ensuring that Afghanistan cannot be a safe haven for al-Qaida or other violent extremists."