Kabul, Afghanistan (CNN) -- The deadly protests in northern Afghanistan over a Quran burning spread to the country's war-torn southern region on Saturday, with provincial government officials reporting at least nine civilians dead and dozens injured.
The violence struck the city of Kandahar when demonstrators took to the streets to protest the torching of Islam's most sacred book by a U.S. church.
The unrest followed a demonstration on Friday in the northern town of Mazar-e Sharif, in which five demonstrators and seven U.N. employees were killed when an angry throng stormed the U.N. compound there.
U.S. President Barack Obama on Saturday extended condolences to the families and loved ones of those killed in Mazar-e Sharif, but also decried the burning of the Quran.
"The desecration of any holy text ... is an act of extreme intolerance and bigotry," he said in a statement released by the White House. "However, to attack and kill innocent people in response is outrageous, and an affront to human decency and dignity."
Besmellah Afghanmal, a Kandahar provincial council member, said hundreds gathered in Kandahar city to protest the Quran burning.
"Today the enemies of peace in Afghanistan killed and injured our people in Kandahar," said a statement from the office of the Kandahar governor.
The demonstration started peacefully, but protesters turned violent, setting fire to a school and vehicles in Kandahar city, said Zalmai Ayoubi, spokesman for the governor of Kandahar province.
Along with the nine deaths, 73 others were injured, the provincial government said.
Ayoubi said Afghan security forces arrested 17 people, including seven who were armed and are suspected of shooting at protesters.
Pastor Terry Jones sparked international controversy last year when his Gainesville, Florida, church planned "International Burn a Quran Day" on the ninth anniversary of the September 11, 2001, attacks on the World Trade Center and the Pentagon.
Jones' church did not host a Quran burning on that day, but the Dove World Outreach Center's website announced an "International Judge the Koran Day" set for last month.
Another post on the site's blog showed an image of a burning book and read, "The event is over, the Koran was found guilty and a copy was burned inside the building."
Some witnesses in Kandahar said protesters were shot by police.
"I saw personally three people who (were) shot to death, and one of them was shot just next to me," protester Shah Meer said.
But police said they neither shot at nor killed anyone.
"There (was) gunfire into the air in order to bring the people under control, and luckily not one has been killed as a result of the gunfire," said Zemarai Bashari, spokesman for the interior ministry.
Meanwhile, a spokesman for the Taliban said the group was not behind any deaths during the event.
"What happened in Kandahar today was the feeling of the nation, and the Islamic movement of the Taliban was not involved in any (violence)," Zabiullah Mojahed said. "It was the Afghan police that killed the innocent people of Kandahar while they were expressing their feeling against the burning of holy Quran in Florida."
The Mazar-e Sharif killings generated worldwide condemnation, from the U.N. Security Council to the Organization of the Islamic Conference, a 57-state group that calls itself the "collective voice of the Muslim world."
Jones in a statement Friday called the assault "a very tragic and criminal action."
Lal Mohammad Ahmadzai, a spokesman for the police in Mazar-e Sharif, told reporters that a number of suspects "who might be the main organizers" had been arrested from the Friday attack
The United Nations says the seven U.N. staffers killed were four Nepalese security guards and three civilians. A U.N. source said the three civilians were from Norway, Sweden and Romania.
U.N. Peacekeeping Director Alain Le Roy said five demonstrators also were killed. He said no Afghan U.N. staff members were among the dead, he said.
"I understand there were hundreds, if not thousands, of demonstrators. Some of them were clearly armed and they stormed into the building," Le Roy said.
He said the security guards tried their best to halt the demonstrators' advance, but were overwhelmed.
Le Roy said it was not clear that the United Nations was the target. "It happened to be the U.N. because the U.N. is on the ground."
Another 24 people were wounded, said Abdul Rauof Taj, security director of Balkh province.
The U.N. Security Council met Friday and issued a statement condemning the attack, which occurred at the operations center of the United Nations Assistance Mission in Afghanistan, or UNAMA.
Haji Sakhi Mohammad, a businessman in Mazar-e Sharif, said the incident began after Friday prayers, when many people joined a protest against the burning of the Quran. People calling "Death to America" marched to the U.N. compound and broke in, he said. Gunfire broke out, and "I saw protesters shot to death," he said
A student in Mazar-e-Sharif said he and his friends joined the protesters, who numbered in the hundreds. "When we reached the UNAMA office, we came under gunfire by Afghan security guards. Protesters became angry and stormed the building."
Pakistani President Asif Ali Zardari condemned the Quran burning during a speech before Pakistan's legislature on March 22.
"May I, at the outset, strongly condemn on behalf of the people of Pakistan and on my own behalf the deliberate desecration of the holy Quran by a fanatic in Florida," he said, according to a transcript of speech. "We condemn this act in the strongest possible words. ... It is a serious setback to the efforts at promoting harmony among civilized communities throughout the world."
CNN's Matiullah Mati and Catherine E. Shoichet contributed to this report