There was no immediate word on any casualties.
Police spokesman Ebadullah Karimi said a suicide bomber in a Toyota Corolla rammed a convoy of foreign troops on the road from Kabul's main airport to a NATO military installation nearby.
He could give no further details.
There was no immediate claim of responsibility, though Taliban insurgents have launched a wave of attacks around the country since the drawdown of most foreign troops last year to a small training force.