Afghan presidential front-runner Abdullah Abdullah escaped an assassination attempt on Friday when two blasts hit his campaign motorcade in Kabul, killing at least four people just ahead of a hotly contested run-off election.

"The first attack was a suicide car bomb on a convoy of Dr Abdullah Abdullah and the second was a mine attack," Sayed Gul Agha Hashemi, head of Kabul police's criminal investigation branch, told said.

A damaged car at the site of a suicide car bomb attack on the convoy of Afghan presidential candidate Abdullah Abdullah. Credit:AFP

Dr Abdullah said he was unhurt, but at least four people were killed and 17 others wounded, according to deputy interior minister Mohammad Ayoub Salangi.

"Four people were killed - one guard of the Abdullah Abdullah campaign team, a traffic policeman and two civilians - and 17 civilians were wounded in two explosions in Kabul," he said on Twitter.