"We don't know at this point if the foreign casualties are military personnel or civilians. They could be from an embassy or a foreign company or anyone," he said.
Attacks have increased in Kabul in the past year as Afghanistan has suffered its bloodiest period since US-led soldiers forced the Taliban movement from power.
In the last bombing in the capital, on August 15, a mine hit a convoy of 4WD vehicles, killing three policemen from the German embassy.
Separately, the Afghan defence minister has revealed that the Afghan military called off a plan to attempt to rescue 23 South Korean hostages shortly after they were captured by the Taliban five weeks ago.
Two of the hostages have since been killed and talks to free the others were have stalled after the movement released two as a "gesture of goodwill".
"From day one, especially from the second day of the Korean hostage crisis, the national army was in position to initiate military action. We wanted to use our first commando battalion, an elite unit," Abdul Rahim Wardak, defence minister, said.
The Taliban split the hostages into small groups early on, officials say, making any rescue bid much more difficult. The captors have repeatedly warned that any military operation would put the hostages' lives at risk.
"A hostage rescue operation is a very complicated operation," Wardak said.
"To make it successful, it needs very elaborate intelligence, inside information. But what happened was the international community asked us not take military action and that was the repeated request of the South Korean government."
The Taliban have demanded that the Afghan government release imprisoned colleagues in return for the hostages. Kabul has refused to give in to the demand, saying that would just encourage more kidnapping.