A suicide bomber rammed a car packed with explosives into a mini-bus carrying foreign aviation workers to the airport in the Afghan capital today, killing at least 12 people including eight South Africans.

A militant group claimed the attack aimed to avenge a film deemed offensive to Islam.

The powerful early morning blast was the first to target Kabul since a video clip of the film was posted on the Internet last week, sparking angry protests across the Muslim world including in Afghanistan.

It was also the second and deadliest attack in Afghanistan that militants have said they carried out as revenge strikes in response to the film.

Haroon Zarghoon, a spokesman for the Islamist militant group Hizb-i-Islami, claimed responsibility for the dawn attack in telephone call to the Associated Press.

He said it was carried out by a 22-year-old woman named Fatima. Suicide bombings carried out by women are extremely rare in Afghanistan, and few if any women drive cars.

"The anti-Islam film hurt our religious sentiments and we cannot tolerate it," Zarghoon said. He said the 22-year-old Fatima volunteered to be the suicide bomber.

"There had been several young men who wanted to take revenge but Fatima also volunteered and we wanted to give a chance to a girl for the attack to tell the world we cannot ignore any anti-Islam attack."

Zarghoon warned of more attacks against foreigners working for NATO and said the group had been seeking targets since a video clip of the film was posted on the Internet last week.

The bombing was a worrisome escalation of violence in the capital, where most attacks are usually blamed on the Haqqani network, a Pakistan-based militant group affiliated with the Taliban and al-Qaeda.