NBC's Atia Abawi reports.
Updated at 8:58 a.m. ET: KABUL, Afghanistan -- Twelve people were killed Friday during protests in Afghanistan over the burning of copies of the Quran at a NATO base, officials said, despite Thursday's written apology from Barack Obama.
Seven people were killed and 50 wounded in the western province of Herat, while two more were killed in Khost in the east. Three people were killed earlier during protests.
On Thursday, two U.S. soldiers were shot dead during a protest by a man wearing an Afghan government soldier's uniform, as a letter from Obama apologizing for the Quran burnings was delivered to Afghan president Hamid Karzai.
The U.S.-led military coalition in Afghanistan says the Qurans and other Islamic texts were sent to a burn pit by mistake.
Protests spread for a third day throughout Afghanistan despite apologies from NATO and U.S. officials for the inadvertent burning of Qurans. NBC's Atia Abawi reports.
Afghan police in Khost, the provincial capital of Khost province, said Friday that an estimated 4,000 protesters were marching toward the governor's compound.
And in the eastern part of Nangarhar province, thousands of people shouted "Death to America!" and burned a cardboard picture of Obama. There was also a smaller protest in the capital Kabul.
NATO's top military commander in Afghanistan, U.S. Gen. John Allen, who apologized Tuesday when the news broke, said Friday that an investigation into the Quran burnings was pushing ahead and called on Afghans to be patient.
"Working together with the Afghan leadership is the only way for us to correct this major error and ensure that it never happens again," Allen said in a statement.
He called on everyone around Afghanistan "to exercise patience and restraint as we continue to gather the facts."
The U.S.-led military coalition says the Muslim holy books were sent by mistake on Feb. 19 to a garbage burn pit at Bagram Air Field, near the capital, and that the case is under investigation.
The explanation and multiple apologies from U.S. officials have yet to calm outrage over the incident, which has also heightened tension between international troops and their Afghan partners.
The death toll since Tuesday now stands at 25, including the two U.S. soldiers.
Meanwhile, Pakistan on Friday urged leaders of the Afghan Taliban movement to enter direct peace negotiations with Kabul, a possible sign that Islamabad is stepping up support for reconciliation in neighboring Afghanistan.
Both Afghan and U.S. officials have long accused Pakistan of using militant groups as proxies in Afghanistan to counter the influence of rival India, allegations Islamabad denies.
Prime Minister Yusuf Raza Gilani said in a statement that Pakistan was "prepared to do whatever it takes" to help the Afghan reconciliation process succeed.
He called on Hizb-i-Islami -- one of Afghanistan's most notorious insurgent factions -- and other militant groups to negotiate peace.
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The Associated Press and Reuters contributed to this report.