KABUL, Afghanistan — Afghans protesting the burning of a Quran at a small Florida church stormed a U.N. compound in northern Afghanistan on Friday and killed at least seven international staff. At least four protesters were also killed.

Afghan authorities suspect insurgents melded into the mob and they announced the arrest of more than 20 people, including a militant they suspect was the ringleader of the assault in Mazar-i-Sharif, the provincial capital of Balkh province.

The suspect was an insurgent from Kapisa province, a hotbed of militancy about 250 miles  southeast of the city, said Rawof Taj, deputy provincial police chief.

The topic of Quran-burning stirred outrage among millions of Muslims and others worldwide after the Rev. Terry Jones' small church, Dove World Outreach Center, threatened to destroy a copy of the holy book last year on the ninth anniversary of the Sept. 11 terror attacks. The pastor backed down but the church in Gainesville, Fla., went through with the burning last month.

About 30 people attended a mock trial staged by the church on March 20 as part of the "International Judge the Quran Day." The church's website stated that after the five-hour process, the Quran "was found guilty and a copy was burned inside the building." A picture on the website shows a book in flames in a small portable fire pit. The church on Friday confirmed that the Quran had been burned.

Jones said Friday he did not feel responsible for the violence. "We wanted to raise awareness of this dangerous religion and dangerous element," he told ABC's "Nightline."  "I think [the Afghanistan attack] proves that there is a radical element of Islam."

In a separate statement, Jones said it was time to "hold Islam accountable" and called on the United States and the U.N. to hold "these countries and people accountable for what they have done as well as for any excuses they may use to promote their terrorist activities."

Some members of Jones' church said they feared they would be targeted for retaliation.

“We have a huge stack of death threats,” Fran Ingram, an assistant at the church, told The New York Times. “We take precautions. I have a handgun. A lot of us have concealed weapons permits. We’re a small church, and we don’t have money to hire security.”

At least four protesters also died in the violence in Mazar-i-Sharif, which is on a list of the first seven areas of the country where Afghan security forces are slated to take over from the U.S.-led coalition starting in July.

Officials at U.N. offices in New York said earlier the final toll could be as high as 20.

Other demonstrations, which were peaceful, were held in Kabul and Herat in western Afghanistan, fueling resentment against the West at a critical moment in the Afghan war.

Protesters burned a U.S. flag at a sports stadium in Herat and chanted "Death to the U.S." and "They broke the heart of Islam." About 100 people gathered at a traffic circle near the U.S. Embassy in Kabul. One protester carried a sign that said: "We want these bloody bastard Americans with all their forces to leave Afghanistan."

Initially, Afghan police reported that eight foreigners had been killed in Mazar-i-Sharif.

Late Friday, Dan McNorton, a U.N. spokesman in Kabul, revised the death toll to seven — four foreign security guards and three other foreigners.

The guards were from Nepal, according to Gen. Daud Daud, commander of Afghan National Police in several northern provinces.

Sweden Foreign Minister Carl Bildt said Joakim Dungel, a 33-year-old Swede who worked at the U.N. office, was among those killed.

Norwegian Defense Ministry spokeswoman Maj. Heidi Langvik-Hansen said Lt. Col. Siri Skare, a 53-year-old female pilot working for the U.N., died in the attack.

A western official, who spoke on condition of anonymity because he wasn't authorized to disclose the information, said the other victim was a citizen of Romania.

The Russian Foreign Ministry said the head of the mission in Mazar-i-Sharif, a Russian citizen, was injured in the attack, but not seriously.

At least two of those killed were beheaded, Reuters said.

Munir Ahmad Farhad, a spokesman in Balkh province, said the protest began peacefully when several hundred demonstrators gathered outside the U.N. mission's compound, choosing an obvious symbol of the international community's involvement in Afghanistan to denounce the Quran's desecration.

It turned violent when some protesters seized the guards' weapons and started shooting, then the crowds stormed the building and set fires that sent plumes of black smoke into the air, he said.

One protester, Ahmad Gul, a 32-year-old teacher in the city, gave a different account. He said the protesters disarmed three guards to prevent any violence from breaking out. Associated Press video showed protesters banging AK-47 rifles on the curb, breaking them into pieces. He said the protesters were killed and wounded by Afghan security forces.

"I disarmed three guards myself and we took out the bullets," Gul said, sternly shaking his finger as he shouted. "With my eyes, I saw them (Afghan security forces) kill two and wound 10." As he talked, he became increasingly indignant and he started shouting: "Death to America!" "We are going to fight."

The United Nations Security Council held an emergency meeting on the deadly attack, which drew condemnations from around the world.

Secretary-General Ban Ki-moon, who is in Nairobi, said it was "a cowardly attack that cannot be justified under any circumstances."

President Barack Obama condemned the attack and underscored the importance of the U.N.'s work in Afghanistan.

"We stress the importance of calm and urge all parties to reject violence and resolve differences through dialogue," Obama said.

At the U.S. State Department, spokesman Mark Toner said the burning of a Quran in Florida was contrary to Americans' respect for Islam and religious tolerance. "This is an isolated act done by a small group of people and ... does not reflect the respect the people of the United States have toward Islam," he said.

Last week, Afghan President Hamid Karzai issued a statement calling the burning a "crime against a religion." He denounced the U.N. attack as a "disrespectful and abhorrent act" and called on the U.S. and the United Nations to bring to justice those who burned the holy book.

The U.N. has been the target of previous attacks.

In October 2010, a suicide car bomber and three armed militants wearing explosives vests and dressed as women attacked a U.N. compound in Herat in western Afghanistan. Afghan security forces killed the attackers and no U.N. employees were harmed. In October 2009, Taliban militants attacked a guesthouse used by United Nations workers in central Kabul. Eight people were killed, including five foreigners working for the U.N.

Separately, the U.S. Department of Defense announced that six U.S. Army soldiers were killed in separate incidents in fighting against insurgents during an operation in eastern Kunar province, which neighbors Pakistan's lawless tribal areas. Insurgents have slowly been filtering back into Afghanistan from safe havens in Pakistan as the spring fighting season gets under way.