There was no immediate claim of responsibility for the attack in a crowded area outside an airport checkpoint, but a security official said it appeared to be aimed at two armoured cars, although it was not clear who was in the vehicles.

The tangled, flaming wreckage of one of the cars lay on its side, as dozens of fire fighters and police gathered. Four civilians were killed, and 17 people wounded, including a woman and a child, said Wahidullah Mayar, a spokesman for the Public Health Ministry.

Kabul was already on high alert following last week's attacks which killed at least 50 civilians and security forces personnel in the worst violence in the Afghan capital in years. The wave of violence comes days after a change of leadership in the Afghan Taliban, who announced the death of their founder, Mullah Mohammad Omar, late last month and named Mullah Mohammad Akhtar Mansour as their new leader.
             
However his swift appointment by a small council of leaders in the Pakistani city of Quetta has angered others in the group, causing rifts within the movement and adding to speculation that the latest wave of violence is linked to the leadership dispute.

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