An Afghan investigation says negligence contributed to the high death toll in the country's deadliest suicide bombing in northern Baghlan province, with some victims hit by gunfire after the blast.

Afghanistan's interior minister, Zarar Ahmad Moqbel, said Tuesday at least three people were treated for gunshot wounds following the November 6 attack.

Victims' families have since requested some of the bodies be exhumed and examined for bullets.

The probe also found that official negligence contributed to the large number of casualties. At least 77 people were killed during the bombing, including six lawmakers and about 60 school children. They were there to greet visiting parliamentarians who were about to tour a sugar factory.

Reports have said the majority of those killed died from gunshots fired by security guards right after the attack.

On Monday, Afghan lawmakers staged a mass walkout to protest the government's response to the bombing.

Opposition figure and speaker of the lower house of parliament, Yunus Qanuni, said the government ignored parliament's demand for the suspension of officials in Baghlan province.

Separately today, Afghan police say a suicide car bomber killed two people in a high security area in the capital, Kabul, when he blew himself up next to an armored car convoy carrying soldiers from the U.S.-led coalition.

A spokesman for the Hezb-e-Islami militant group claimed responsibility for the attack.

Some information for this report was provided by AFP, AP and Reuters.