Violent protests over the burning of a Koran spread to the heart of Taliban country Saturday, as clashes between demonstrators and Afghan police in Kandahar left at least nine people dead and more than 90 injured, according to Afghan officials.

The clashes marked the second consecutive day that mobs had thronged the streets of major Afghan cities to protest the burning of Islam’s holy book last month by a Florida pastor. On Friday, a mob attacked a U.N. compound in the normally placid northern city of Mazar-e Sharif and killed seven U.N. employees. The Koran burning also prompted more peaceful demonstrations in the capital, Kabul, in the western city of Herat and in the northern province of Takhar.

The protests have tapped into a well of frustration among many Afghans about the decade-long presence of U.S. and international troops on their soil. The sentiments expressed in signs and chants have denounced America and President Obama and called on troops to leave the country.

The Taliban has played a murky role in the protests so far. Afghan and Western officials allege its fighters have infiltrated crowds to encourage violence, but it has been content in public statements to cheer on the protesters without claiming responsibility for the unrest.

The demonstrations have also been fueled by mullahs, who in their Friday sermons took a cue from President Hamid Karzai’s denunciation of pastor Terry Jones’s church four days after the Koran was burned. Afghan mosques — even mainstream, publicly funded ones — have emerged as a powerful anti-American voice in the country, and the imams regularly call for U.S. troops to withdraw.

The protests in Kandahar began Saturday morning with a few hundred people in a downtown bazaar not far from the offices of the provincial government. As the protesters moved around the city, the crowds grew larger. Some protesters said they had intended to approach the local U.N. office but were blocked by Afghan security forces.

Some of the participants were armed with guns and sticks and waving white flags, the banner of the Taliban. They set fire to a girls’ high school and torched buses and cars. Shops were shuttered, and security forces blocked roads to try to quell the violence.

The police opened fire on the crowds, the protesters said. The city’s provincial director of public health, Abdul Qayoum Pukhla, said all of the injured who came or were brought to Kandahar hospitals had suffered gunshot wounds.

“We’re still receiving wounded people,” he said after hours of violence.

The provincial police chief, Khan Mohammad Mojayed, denied that his men were firing on protesters, saying they were shooting in the air to disperse the crowd.

“The police have to protect the civilians,” he said. “Among the protesters, there were also some armed men with sticks and guns. They were stopping the cars and damaging them and opening fire.”

The provincial governor’s office issued a statement blaming the mayhem on “wicked and destructive people” among the protesters but endorsed people’s right to condemn the Koran burning.

Jan Aghan, a 28-year-old shopkeeper in Kandahar, said he took part to “show the infidels that we are unhappy with their actions.” He said that the protesters wanted to go to the U.N. office but that the “Afghan slave government and the cruel Americans” blocked their path.

“We think the Karzai government doesn’t want any protest against the people who burnt our holy book in America,” he said. “We are waiting to find a way to reach to the [U.N.] office and announce our objections.”

The governor’s spokesman, Zalmay Ayoubi, blamed the unrest on the “idiot, infidel, blasphemous Americans,” and said the people have a right to show their anger about the desecration of the Koran.

Staffan de Mistura, the U.N. envoy in Afghanistan, told reporters that the authorities in Kandahar, unlike those in Mazar-e Sharif, “were not taken by surprise” by the protesters and succeeded in keeping them away from the U.N. building.

De Mistura, who arrived back in Kabul late Saturday after touring the wreckage of his offices in Mazar-e Sharif, said that the Afghan police there had not provided a proper cordon to keep protesters at bay and that the Afghan government needs to pay “more attention to the security of the international community present here, especially the civilian one.”

He offered the most detailed account yet of how seven of the 12 U.N. staff members inside the compound in Mazar-e Sharif had died Friday evening. The mob, he said, was led by seven to 15 Taliban infiltrators with handguns who had come from other provinces to join the protest. After chanting and throwing rocks, the crowd broke through the outer door, despite gunfire from the Afghan police on the perimeter, and the insurgents entered the compound.

The six Nepalese guards had orders not to shoot . “The U.N. does not shoot at crowds, even if they are threatening,” de Mistura said. All but two of them died trying to protect the compound and the six civilian staff members , two Afghans and four foreigners, who were inside at the time.

As the mob surged in, the two Afghan staff members blended into the crowd and escaped. The mob looted the offices and set fire to cars and the generator, which cut the power and plunged the compound into darkness. The four international workers ran down to a bunker meant to protect against bomb blasts, de Mistura said, but the protesters pried open the door.

Members of the mob beat the head of the U.N. office, Pavel Ershov, a Russian, until he persuaded them, by speaking in Dari, that he was a Muslim and escaped, de Mistura said. The mob found the other three: Joakim Dungel, a Swedish human rights worker; Lt. Col. Siri Skare, a Norwegian who was advising the police; and Filaret Motco, a Romanian political officer. They were shot one after another and one’s throat was also slashed, de Mistura said.

De Mistura said he would “temporarily redeploy” 11 remaining international staff members from Mazar-e Sharif back to Kabul until a new office can be established.

“I am profoundly sad, and I am also shocked by what I saw, but we do continue our work. We are not going to be deterred,” he said.

Also Saturday morning, Taliban fighters attacked the gate of a NATO military base, Camp Phoenix, on the outskirts of Kabul but failed to inflict serious damage or breach the compound walls, according to NATO and Afghan officials. At least two of the attackers were killed.

Special correspondent Javed Hamdard contributed to this report.