KABUL, Afghanistan — President Obama apologized Thursday for the burning of copies of the Muslim holy book at a U.S. military base this week, as violent protests raging nationwide led a man dressed in an Afghan army uniform to kill two U.S. troops.
The Afghans' furious response to the Koran burning — three days of riots in several cities nationwide — reflected the anger at what they perceive as foreign forces disrespect for Afghan laws and culture.
In a letter sent to Afghan President Hamid Karzai, Mr. Obama expressed his administration's "regret and apologies over the incident in which religious materials were unintentionally mishandled," White House National Security Council spokesman Tommy Vietor said. He added that the letter was delivered by Ryan Crocker, the U.S. ambassador to Afghanistan, Thursday afternoon.
Mr. Karzai's office said Mr. Obama called the Koran burnings "inadvertent," adding that the U.S. "will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible."
U.S. apologies for the desecration — and an appeal from Mr. Karzai for calm — have failed to temper the anger of Afghans, who staged rallies in seven provinces Thursday, sparking clashes with Afghan police and security forces that left at least five demonstrators dead. Seven protesters were killed in clashes on Wednesday.
The two NATO service members were killed in eastern Afghanistan by a man dressed in an Afghan army uniform. Both troops were Americans, according to a U.S. official, who confirmed their nationalities on condition of anonymity because he was not authorized to disclose the information.
Mohammad Hassan, an official in Nangarhar province, where the shooting took place, said the two Americans were shot by an Afghan soldier after soldiers fired in the air to disperse protesters outside a U.S. base in the Khogyani district. Two protesters also were killed in the ensuing gunfire, Afghan officials said.
A rising number of Afghan security forces, or militants wearing their uniforms, have shot and killed U.S. and NATO service members.
The Taliban on Thursday called on Afghans to attack foreign troops, and their spokesman has issued a statement ordering its commanders to embrace and protect the families of any Afghan policeman or soldier who turns his gun on foreign troops.
"Call them heroes," he said.
Protesters also rioted outside a U.S. base in Mehterlam, the capital of Laghman province. Police broke up a demonstration using water cannons and batons after protesters tried to storm the base.
"Hundreds of our people in Laghman province gathered because of the burning of the holy book by the Americans," protester Mohammad Issa said.
"Everyone is so emotional. The burning of the Koran broke our hearts, and we are attacking the PRT because they are American," he said, using the acronym for the provincial reconstruction team.
In Oslo, Norwegian military spokesman Ivar Moen said a Norwegian soldier was wounded after demonstrators threw a hand grenade into a military base in Maimanah, in northwestern Faryab province, where Norwegian, Latvian, Afghan and U.S. troops are deployed.
The soldier was wounded after up to 200 demonstrators hurled rocks at the base and shouted epithets. Norwegian troops responded with warning shots and tear gas. Mr. Moen said the demonstration was over, but new protests are expected tomorrow.
In the city of Baghlan in the north, clashes between police and protesters attacking the police headquarters left one person dead. Police said 10 officers were also wounded, two from gunshot wounds.
Police said another two protesters were killed and six wounded in another exchange of gunfire during a protest in southern Uruzgan province.
The riots erupted Tuesday after Afghan workers at the main American military base, Bagram Airfield, saw soldiers dumping books in a pit where garbage is burned and noticed Korans and other religious material among the trash.
The top U.S. and NATO commander, Gen. John Allen, quickly issued an apology and telephoned Mr. Karzai and major news organizations to explain that a collection of religious materials, including Korans, mistakenly had been sent to be incinerated. As soon as someone realized what they were burning, they stopped and retrieved what was left, Gen. Allen said.
Mr. Karzai also met Thursday with parliamentarians — many of whom had called Wednesday for Afghans to wage a holy war against international forces. He told them that a U.S. officer responsible for the incident "didn't understand" what he was doing and the United States "accepted the mistake of its officer."
He commended the U.S. government for "acting quickly regarding this issue and apologizing." Mr. Karzai said that he was most concerned with making sure that such acts are not repeated.
Four copies of the Koran were burned before the incineration was halted, according to initial Afghan government reports.
NATO and Afghan investigators Wednesday visited the Parwan detention facility from which the Korans were taken. U.S. officials said they had been removed from the shelves of the facility's library because they contained extremist messages or inscriptions. The White House said it was an accident that they were sent to be burned.
• Associated Press photographer Rahmat Gul in Mehterlam, Afghanistan, and writers Malin Rising in Oslo and Pauline Jelinek in Washington contributed to this article.