A female bomber killed 12 people, including South Africans, in Kabul on Tuesday in the deadliest single attack claimed to avenge a US film that has sparked a week of deadly protests across the Muslim world.
The bombing brings to more than 30 the number of people now killed in a violent backlash over a YouTube trailer for the film, "Innocence of Muslims", believed to have been produced by a small group of extremist Christians.
Security officials said nine foreigners were among those killed on a major highway leading to Kabul airport when the bomber blew her station wagon up alongside a minivan carrying foreign workers.
The South African foreign ministry confirmed that eight of its citizens, all believed to have been men working for a private aviation company, were killed.
An AFP photographer saw at least six bodies lying among the wreckage of a gutted minivan, and another vehicle destroyed by flames still burning in the middle of the highway, with debris flung all around.
Hezb-i-Islami, the second largest insurgent group after the Taliban who have been fighting US-led troops and the government for 10 years, claimed the attack.
"The bombing was in retaliation for the insult to our Prophet," spokesman Zubair Sidiqi told AFP in a telephone call from an undisclosed location.
It is extremely rare for the faction to claim a suicide attack in Afghanistan.
Taliban fighters last week stormed a British-run airfield, killing two US Marines and destroying six US fighter jets also to avenge the film.
A week of furious protests outside US embassies and other American symbols in at least 20 countries have killed 19 other people, including the American ambassador to Libya and three other US diplomats in the North African country.
In Lebanon, the head of Hezbollah made a rare public appearance to warn of "very dangerous" repercussions if the entire film is released.
Tens of thousands of demonstrators poured into the streets of southern Beirut to denounce the film at the request of Nasrallah, who has called for a week of protests over the film, describing it as the "worst attack ever on Islam".
"The US must understand that releasing the entire film will have dangerous, very dangerous, repercussions around the world," he told the rally.
The filmmaker Nakoula Basseley Nakoula, a 55-year-old Egyptian Copt and fraudster who was sentenced to 21 months in prison in the US in June 2010, has not been seen since Saturday when he was questioned.
The risks now facing those involved in the production of the film were underlined when a cleric in Egypt called on Monday for the deaths of all those involved in its making.
Before dawn on Monday, officers from the Los Angeles County sheriff's department escorted four members of Nakoula's family to join him in hiding.
In Pakistan, two protesters died after demonstrating against the film in the northwest, close to the Afghan border, and outside the US consulate in Karachi.
Afghanistan, Bangladesh and Pakistan also blocked access to YouTube, following the video-sharing website's failure to take down the anti-Islam film.
Google, which owns YouTube, has also barred access to the film in Egypt, India, Indonesia, Libya and Malaysia.
On Tuesday, fresh protests erupted in Afghanistan and Indonesia. Several hundred university students threw stones at police and set fire to pictures of US President Barack Obama in the northern Afghan city of Kunduz.
In the second protest in as many days outside the US diplomatic mission in the Indonesian city of Medan, angry men torched an American flag and burned tyres.
"Under Islamic law the filmmaker who insulted the Prophet Mohammed must be punished by death," one of the protesters told the crowd.
Violent demonstrations have spread this week after police last Friday battled to defend US missions from mobs in Egypt, Lebanon, Sudan, Tunisia and Yemen.
The United States has deployed counter-terror Marine units to Libya to protect its embassy in Tripoli and stationed two destroyers off the North African coast.
On September 11, its consulate in the eastern Libyan city of Benghazi came under sustained attack, killing four Americans, including ambassador Chris Stevens.
A Marine unit was also dispatched to protect the US embassy in Yemen, where police shot dead four protesters and wounded 34 others on Thursday as a mob breached its perimeter. There were more protests in Yemen on Monday.
The United States has evacuated all non-essential staff and family members from Sudan and Tunisia and warned US citizens against travel to the two countries.