Twelve people were killed near Kabul’s airport Tuesday when a suicide car bomber rammed into a minivan carrying foreign air-charter workers, Afghan officials said. A Pakistan-based militant group said it carried out the attack to avenge a YouTube video that defames the Muslim prophet Muhammad.

Many of the victims were contract personnel with Air Charter Service, a British-based company that provides services to the U.S. Agency for International Development and other organizations in Afghanistan, U.S. Embassy officials said. It was not known whether those behind the attack knew of connections to the embassy.

The attack came as al-Qaeda’s branch in North Africa called on Muslims to attack U.S. diplomats and step up protests against the video. Demonstrations have abated in Egypt, Tunisia and a number of other Islamic nations, but Muslims protesting the video battled police Tuesday in Indian-controlled Kashmir, and anti-American demonstrators held small rallies in Indonesia, the Associated Press reported.

The Afghan Interior Ministry confirmed the death toll in Kabul, which included the van’s Afghan driver and two Afghan bystanders, according to news service reports. President Hamid Karzai said in a statement that eight of the dead were South African and one was from Kyrgyzstan.

Gen. Mohammad Zahir, head of the Kabul police force’s criminal investigations department, said the blast also injured 10 people on the busy road to heavily fortified Kabul International Airport.

The bomber was a young Kabul woman, according to Haroon Zarghhon, a spokesman for Hezb-i-Islami (Party of Islam), which asserted responsibility for the attack. Hezb-i-Islami is a maverick Islamist group that has factions allied with the Taliban but also has members serving in the Afghan government.

Air Charter Service has a contract with the U.S. Embassy in Kabul to ferry USAID officials around Afghanistan. Police initially reported that the van belonged to the DHL delivery company, but a DHL spokeswoman in the United States said all of the firm’s employees were alive and accounted for.

A day before the blast, violent protests erupted in Kabul over the incendiary, Islam-insulting “Innocence of Muslims” video that has provoked Muslim outrage worldwide. The suicide attack, the second in Kabul this month, coincides with an escalation of “insider” shootings in which Afghan security forces have gunned down four American service members and two British troops.

“I am so happy that the suicide bomber killed foreigners because they insulted our holy prophet,” said eyewitness Ameer Mohammad, 58, who was running to the blast site.

The road is also heavily used by schoolchildren, but it appeared that none were killed, because they were on a sidewalk on the other side of the road from the blast. A 12-year-old student named Rameen, who was on his way to school, said: “I heard a horrible explosion. I fell down to the ground. When I stood up, I saw dead bodies.”

A faction of Hezb-i-Islami headed by Gulbuddin Hekmatyar was a Washington-supported group battling the Soviets during their occupation of Afghanistan in the 1980s. Today it shares many elements of the Taliban ideology. In some parts of the country, it cooperates with the Taliban insurgents in the campaign against foreign and Afghan forces despite some differences.

But the group has rarely claimed responsibility for past suicide attacks. Only two attacks by women bombers have occurred in recent memory. The Taliban said they were sympathizers with the cause of driving out foreign forces that support the Afghan government.

In a statement Tuesday, al-Qaeda in the Islamic Maghreb, the terrorist network’s branch in North Africa, threatened attacks against Americans in Algeria, Tunisia, Morocco and Mauritania, the AP reported. The group praised the killing of J. Christopher Stevens, the U.S. ambassador to Libya, in a Sept. 11 attack on the U.S. Consulate in Benghazi. It urged Muslims to kill or expel other American diplomats to “purge our land of their filth in revenge for the honor of the prophet.”

Al-Qaeda in the Arabian Peninsula, which is based in Yemen and ranks as the strongest al-Qaeda branch in the Middle East, has also called for more attacks on U.S. diplomatic facilities.

Javed Hamdard and Sayed Salahuddin contributed to this report.