Afghans chant anti-American slogans during a demonstration to condemn the burning of a copy of the Muslim holy book by a US pastor, in Mazar-i- Sharif April 1, 2011. [Photo/Agencies]

KABUL, Afghanistan - Afghans angry over the burning of a Quran at a small Florida church stormed a UN compound in northern Afghanistan on Friday, killing seven foreigners, including four Nepalese guards.

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 (400 kilometers) 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 Outreach Center, threatened to destroy a copy of the holy book last year. The pastor backed down but the church in Gainesville, Florida, went through with the burning last month.

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

UN peacekeeping chief Alain LeRoy said the top UN envoy in Afghanistan, Staffan De Mistura, who is in Mazar-i-Sharif, believes "the UN was not the target."

"They wanted to find an international target and the UN was the one there in Mazar-i-Sharif," LeRoy told reporters at UN headquarters in New York.

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

Late on Friday, Dan McNorton, a spokesman for the United Nations Assistance Mission in Afghanistan 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 UN 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 UN, died in the attack.

LeRoy said the other victim was a citizen of Romania and that a number of UN personnel were injured and were being evacuated.

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.

Police who went to investigate, said the UN compound was littered with broken glass and bullet casings.

Abdul Karim, a police officer in the city, said he saw the bullet-riddled bodies of three Nepalese guards lying in the yard and a fourth on the first floor.

He said another victim with a serious head wound died on a stairway to the basement of the compound. A man who was killed inside a room had severe wounds to his face and body, Karim said.

Munir Ahmad Farhad, a spokesman in Balkh province, said the protest began peacefully when several hundred demonstrators gathered outside the UN 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."

LeRoy, the UN peacekeeping chief, said the security guards, all Gurkhas, "tried their best" but were unable to prevent the large number of demonstrators, some armed, from storming the UN compound.

The UN Security Council held an emergency meeting late Friday and condemned the attack "in the strongest terms."

The UN's most powerful body also condemned "all incitement to and acts of violence" and called on the Afghan government to bring those responsible to justice and take steps to protect UN personnel and premises.

Secretary-General Ban Ki-moon, who is in Nairobi, said it was "an outrageous and cowardly attack against UN staff, which cannot be justified under any circumstances and I condemn in the strongest possible terms."

He instructed De Mistura to assess the situation and take any "necessary measures to ensure the safety of all UN staff."

LeRoy said UN officials would be reviewing security for UN personnel in Afghanistan.

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

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

Last week, Afghan President Hamid Karzai issued a statement calling the burning a "crime against a religion." He denounced the UN attack as a "disrespectful and abhorrent act" and called on the US and the United Nations to bring to justice those who burned the holy book. Karzai issued a statement late Friday calling the killings an "inhumane act" that was "against the values of Islam and Afghans." He said he planned to call officials at UN headquarters to express his regret and condolences from the people of Afghanistan.

The UN 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 UN compound in Herat in western Afghanistan. Afghan sbul, Edith M. Lederer at the UN and Mitch Stacy in Tampa, Florida, contributed to this report.