Herat , 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 . Four civilians were killed and 50 injured amid protests near the United Nations office in Kunduz , said Saad Mokhtar , head of the city 's health department . Twelve police officers were among the wounded . Gulam Mohamad Farhad , the intelligence head of Kunduz , said the protesters tried to burn down the U.N. building . The U.N. 's Afghan mission said all its staff in Kunduz and throughout the country are `` unhurt . '' It denounced the attack on its compound , regretted the casualties and thanked Afghan police for their timely response to the violent protests . The mission also said it understands Muslim anger over the Quran desecration . `` At the same time , we call upon those who would wish to express their legitimate religious sentiments to reject calls to violence , to exercise self-restraint and to avoid resorting to protests and demonstrations in order not to allow the enemies of peace to take advantage of the situation , '' the mission said in a statement . The protests began after NATO troops recently burned Qurans at Bagram Airfield . The burnings sent throngs of protesters to the streets and military bases , some chanting , `` Death to America . '' 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 . '' American officials , including President Barack Obama , apologized and said burning them was an unintentional error , but protests raged on nonetheless . In a letter to his Afghan counterpart , President Hamid Karzai , Obama called the act `` inadvertent . '' Four U.S. service members have died in Afghanistan since the outrage turned violent . A gunman Saturday shot dead two American officers inside the Afghan interior ministry in Kabul and escaped . A Taliban spokesman said the attack , for which the group claimed responsibility , was in response to the recent burnings . NATO and Afghan officials are investigating and have not confirmed involvement by the Islamist militant group . The commander of U.S. forces in Afghanistan , Gen. John Allen , addressed the Quran burning 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 . Allen called on troops to `` show the Afghan people that as bad as that act was at Bagram , it was unintentional , and Americans and ISAF soldiers do not stand for this . We stand for something greater than that . '' The protests on 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 . 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 burning at Bagram was not the first time that damaging Qurans -- or even the threat to do so -- has provoked angry Muslim reaction . Terry Jones , the pastor of a tiny evangelical church in Florida , announced plans to burn the Muslim holy book on the ninth anniversary of the September 11 , 2001 , attacks on the United States . He was persuaded not to do it at the time , but he made good on the threat six months later . Two weeks after that , protesters in northern Afghanistan attacked a U.N compound , leaving 12 people dead . In Kandahar , three people were killed in one demonstration , and nine in another when police and stone-throwing demonstrators clashed . `` The first belief among Muslims of all types is that the Quran is the word of God , '' said Shainool Jiwa , of the Institute of Ismaili Studies in London . `` The words themselves , the typing , takes on a level of sanctity . There is a sacredness about it . '' But , she said , violent reactions to its burning are as much a sign of the times as an expression of faith . `` There is a history behind this . It 's much more reflective of the times we are in , the protests and anger , '' she said . `` This whole issue has become politicized . '' CNN 's Josh Levs and Richard Allen Greene contributed to this report .
Four civilians are killed and 50 people are injured in Kunduz , a health official says . The Taliban claim responsibility for the attack on Saturday. The protests start after NATO troops burn Qurans at Bagram Airfield . Taliban says Saturday 's killing of two U.S. military officers is linked to burning .