Twelve people have been killed by two explosions targeting Afghan presidential front-runner Abdullah Abdullah in an attack that triggered strong international condemnation. 

Mr Abdullah survived the assassination attempt yesterday when the blasts, including a suicide bombing, targeted his campaign motorcade in Kabul ahead of next week's hotly contested run-off election.

It was the second attack on Abdullah during Afghanistan's fractious election season, which has seen an uptick in violence with Taliban militants threatening to disrupt the polls.

Up to 40 people have been injured.

The United Nations Security Council condemned the attack strongly, calling for an orderly transition to a new government in Afghanistan.

The US also denounced the attack, saying that "the Afghan people deserve democracy -- which they'll be exercising next week -- not violence".

No one has thus far claimed responsibility for the assassination attempt but Taliban militants have vowed to disrupt the 14 June run-off election.

Mr Abdullah fell short of the 50%  threshold needed for an outright victory in the April first round and will face former World Bank economist Ashraf Ghani in the run-off.