Thousands of Afghans staged new demonstrations Friday over the burning of Qurans at a U.S. military base in Afghanistan, evidence that President Barack Obama's apology has so far failed to quiet the outrage over the incident.

About 4,000 protesters marched toward the governor's compound in Khost, the capital of Khost province, police said. In the eastern part of Nangarhar province, several thousand shouted "Death to America!" and burned a cardboard picture of Obama.

In the capital Kabul, about 100 protesters gathered near the Ministry of Defense but scattered when Afghan soldiers fired in the air. One protester suffered a bullet wound in his right leg.

Anti-American protesters also gathered in several other locations around Kabul, including in the city's east, where a demonstrator, his clothes covered in blood, was carried from the scene as about 200 police tried to push the crowd back.

"We don't care about Obama's apology," said Kamaluddin, a 25-year-old Kabul protester who uses only one name. "We have to protest to be responsible to our god. They are burning our Quran. An apology is not enough."

Afghan security forces were put on high alert to deal with demonstrations that were expected around the country after Friday prayers.

U.S. Gen. John Allen, the top commander of U.S. and NATO troops in Afghanistan, said an investigation into the Quran burning incident at Bagram Air Field was under way and called on Afghans to be patient and exercise restraint.

"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 "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, north of the capital.

Despite Afghan President Hamid Karzai's appeal for calm, thousands of protesters, some shouting "Long live Islam!" and "Death to America!" rallied Thursday in the capital and in seven of Afghanistan's 34 provinces. At least five protesters were killed.

The deadliest protest was held outside an American base in the Khogyani district of Nangarhar province. Two protesters were killed by Afghan police there and an Afghan soldier turned his gun on U.S. troops, killing two Americans. Elsewhere, a Norwegian soldier was wounded by a hand grenade hurled into a coalition compound.

The unrest started Tuesday, when Afghan workers at the sprawling American base noticed that Qurans and other Islamic texts were in the trash that coalition troops dumped into a pit where garbage is burned. Some Afghan workers burned their fingers as they tried to salvage some of the books. Afghan government officials said initial reports indicated four Qurans were burned.

The materials had been taken from a library at Parwan Detention Facility, which adjoins the base, because they contained extremist messages or inscriptions. Writing inside a Quran is forbidden in the Islamic faith, although it was unclear whether the handwritten messages were found in the holy book or other reading materials.

A military official said it appeared that detainees at the prison were exchanging messages by making notations in the texts.

A delegation of Afghan religious leaders, lawmakers and government representatives visited Bagram as part of the investigation. They issued a statement late Thursday calling for an end to protests and accused insurgents of infiltrating the gatherings to foment violence. They said they expected those responsible for the Quran burning to be prosecuted through the U.S. military court system.

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Associated Press photographer Rahmat Gul in Nangarhar contributed to this report.