Kabul, Afghanistan ? Afghans angry over the burning of a Quran at a small Florida church stormed a U.N. 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 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, Fla., 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 U.S.-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 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.”

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

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