KABUL, Afghanistan — Afghan President Hamid Karzai appealed for calm Wednesday after clashes in several cities between Afghan security forces and protesters furious over the burning of Muslim holy books at a U.S. military base left seven people dead.

The anger over the Qur'an burning has sparked two days of protests across Afghanistan and tapped into anti-foreign sentiment fueled by a popular perception that U.S. and Western troops disrespect Afghan culture and Islam. The demonstrations prompted the U.S. to lock down its embassy and bar its staff from travelling.

The Afghan Interior Ministry said in a statement that seven people were killed -- four in clashes in the eastern province of Parwan, one at a U.S. base outside Kabul, and one each in Jalalabad and Logar provinces. It said an investigation was under way to determine what happened.

"The people have the right to protest peacefully, but I appeal to my countrymen not to resort to violence," Karzai said in a statement. He also called on the Afghan security forces to protect the protesters, not battle them.

Karzai said he shared the Afghan people's pain at hearing of the Qur'an desecration, but asked them to "please be patient and wait for the end of the investigation."

The demonstration in Kabul drew thousands of protesters who chanted "Death to America," hurled rocks and set tires alight outside a complex that is home to foreign contractors, police and some coalition military forces. Nearby, angry demonstrators set a fuel truck ablaze on a main highway running east out of the city, sending black smoke billowing into the air.

The U.S. apologized Tuesday for burning the copies of the Qur'an, which had been pulled from the shelves of the Parwan Detention Facility, adjoining Bagram Air Field, because they contained extremist messages or inscriptions.

U.S. Gen. John Allen, the top commander of American and NATO forces in Afghanistan, said after the books had been mistakenly given to troops to be burned at a garbage pit without realizing it.

"It was not a decision that was made because they were religious materials," Allen said Tuesday, one day after Afghan workers at the garbage pit found the books. "It was not a decision that was made with respect to the faith of Islam. It was a mistake. It was an error. The moment we found out about it we immediately stopped and we intervened."

A Western military official with knowledge of the incident said it appeared that the copies of the Qur'an and other Islamic readings in the library were being used to fuel extremism, and that detainees were writing on the documents to exchange extremist messages. He spoke on condition of anonymity because he was not authorized to release the information.

As Wednesday's rally in Kabul turned violent, city police chief Mohammad Ayub Salangi arrived at the scene with hundreds of reinforcements who broke up the protest.

"They have the right to demonstrate, but they have to do it in accordance with the law," said Salangi's deputy, Daud Amin. "It is their right to demonstrate. ... We are also Muslim and we say it was a wrong action from the Islamic point of view."

Several miles (kilometres) away, hundreds of protesters were throwing rocks at Camp Phoenix, a U.S. military base, said Kabul provincial police spokesman Ashmatullah Stanekzai. Shots were also fired in the air at Camp Phoenix.

After the Qur'an burning was made public Tuesday, more than 2,000 Afghans protested outside the Bagram air base near the capital.

In Parwan, provincial police chief Akram Bigzad said about 2,000 protesters were demonstrating outside a district headquarters when some of them opened fire with weapons.

"In the crowd there were rebels and Taliban who had weapons. They opened fire and fighting started. Four were killed and 10 were wounded. They are Talib," Bigzad said.

A protest in Logar province also turned violent after someone in a group of about 300 demonstrators opened fire on police. Police returned fire, killing one protester, said provincial police chief Gen. Ghulam Sakhi Roogh Lawanay.

Two protesters and two police officers were also wounded, he added. He said the protesters had come from neighbouring Wardak province, an insurgent hotbed.

Lawanay said a protest by about 400 people in Logar's capital Pule Alam ended peacefully.