A suicide bomber has killed at least four people and wounded several others in an attack on a vehicle carrying national security officials in Kabul.

An interior ministry official confirms the attack but could not say immediately how many people had been killed or wounded adding that there was no immediate claim of responsibility for the attack.

The attack underscores a worsening security situation nearly two years after NATO formally ended its combat operations in Afghanistan.

Last week, four people were killed and 128 others were wounded when a suicide bomber drove truck loaded with explosives into the German consulate in the northern city of Mazar-I-Sharif.