Ten people were also wounded in the blast -- four policewomen and a policeman, plus five other civilians -- near the civilian airport serving the western city of Herat.

The latest deaths came the day after the United Nations released figures saying that violent incidents in the Afghan war increased nearly 40 percent in the first eight months of this year compared to the same period last year.

In an unusual step, the NATO-led International Security Assistance Force issued a statement in response saying it found the figures "inconsistent with the data that we have collected".

Mohammad Rafiq Shaheer, a spokesman for Herat hospital, said: "A remote controlled mine explosion on a police vehicle on Herat airport road has killed three people, two policewomen and a civilian, and wounded 10 people, four policewomen and a policeman and five other civilians."

He added that the attack took place at around 8:00am.

Noor Khan Neikzad, spokesman for the police chief in Herat, confirmed the blast but said he did not have the toll.