Kabul

Kabul, Afghanistan (CNN) -- Hundreds of protesters took to the streets Saturday across Afghanistan, the fifth day of demonstrations over the burning of Qurans at a U.S. base, officials said.

Three civilians were killed and 50 injured Saturday amid protests near the U.N. office in Kunduz, the head of the city's health department said. Saad Mokhtar said the injured included police.

Gulam Mohamad Farhad, the intelligence head of Kunduz, said the protesters tried to burn down the U.N. building.

The fresh protests Saturday took place in various provinces, including Laghman, Paktika, Baghlan and Nurestan, according to a spokesman for the interior ministry.

In Laghman province, at least 15 people were injured when hundreds of protesters tried to attack the governor's house and office, authorities said.

Police and soldiers intervened, with some injured in the confrontation, said Abdul Rahman Sarjang, a local police chief. Two civilians and an officer were in critical condition, Sarjang said.

But protests in most of the northern regions ended peacefully, police spokesman Lal Mohamed Ahmadzai said.

Deadly anti-American protests erupted this week after NATO troops burned Qurans at Bagram Airfield, officials said. The burnings sent throngs of protesters to the streets and military bases, some chanting, "Death to America."

American officials, including President Barack Obama, apologized and said it was an unintentional error, but protests raged on nonetheless.
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In a letter to his Afghan counterpart, President Hamid Karzai, Obama called the act "inadvertent."

"We will take the appropriate steps to avoid any recurrence, including holding accountable those responsible," Obama said in the letter delivered by Ryan Crocker, the U.S. ambassador to Afghanistan.

At least eight people were killed and 27 wounded in protests Friday, mostly in Herat province, according to Sediq Sediqqi, spokesman for the interior ministry.

No international coalition members have been wounded in the protests, NATO's International Security Assistance Force said.

The commander of U.S. forces in Afghanistan, Gen. John Allen, addressed the issue during a visit to a military base where two U.S. soldiers were killed Thursday by a man wearing an Afghan National Army uniform. A protest over the burning of Qurans was taking place outside the base at the time of the killings.

"Now is not the time for vengeance," he said. "Now is the time to look deep inside your souls, remember your mission, remember your discipline, remember who you are. We'll come through this together as a unit."

Allen urged troops to show Afghans that the move was unintentional.

"Americans and ISAF soldiers do not stand for this. We stand for something greater than that," he said.

A military official said the materials burned were removed from a detainee center's library because they had "extremist inscriptions" on them and there was "an appearance that these documents were being used to facilitate extremist communications."

Muslims believe the Quran is the word of God, so holy that people should wash their hands before touching the sacred book.