A female suicide bomber killed 12 people 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 attack 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 and close to a wedding hall when the bomber blew her station wagon up alongside a minivan carrying foreign workers.
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 carried out by a woman named Fatima. The bombing was in retaliation for the insult to our Prophet," spokesman Zubair Sidiqi told AFP in a telephone from an undisclosed location.
It is extremely rare for the faction to claim a suicide attack in Afghanistan. It is also rare for women to carry out suicide attacks.
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 Shiite Muslim movement Hezbollah, which is blacklisted in the United States as a terrorist organisation, made a rare public appearance to warn of "very dangerous" repercussions if the film is released in its entirety.
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 by his US parole officer.
The risks now facing those involved in the production of the film, which depicts the Prophet Mohammed as a thuggish womaniser, were underlined when a Salafist cleric in Egypt called 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.
"I issue a fatwa and call on the Muslim youth in America and Europe to do this duty, which is to kill the director, the producer and the actors and everyone who helped and promoted the film," said the Egyptian cleric, Ahmad Fouad Ashoush.
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.
The US embassy in the capital Islamabad closed on Monday because of the risk of demonstrations and diplomats have been banned from all but essential travel.
Pakistan has also blocked access to YouTube, following the video-sharing website's failure to take down the anti-Islam film.
Similar measures have been taken in Afghanistan. Google, which owns YouTube, has also barred access to the film in Egypt, India, Indonesia, Libya and Malaysia.
There have been violent demonstrations this week in Kabul and Jakarta, spreading from deadly demonstrations on Friday that saw police battle 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.