Afghanistan's Interior Ministry says only a "small number" of the victims were hit by gunfire, but an Afghan official in Baghlan province told The Associated Press that bodyguards were "raining bullets" on the crowd.
The suicide bomb contained ball bearings, the Interior Ministry said, which may have caused wounds that look like bullet holes.
An Afghan doctor who treated patients after the Nov. 6 blast, meanwhile, told the AP that a high-ranking government official told him not to publicly reveal the number of gunfire victims, suggesting a possible government cover-up.
Separate teams of U.N. investigators have uncovered conflicting information about the number of people hit by gunfire and are trying to reconcile the differences, according to two Western officials who have seen the internal reports. The two spoke to the AP on condition they not be identified talking about preliminary findings.
But at least one of those reports - based on interviews with witnesses and medical authorities and a reconstruction of the bomb scene - says that of the roughly 77 people killed and 100 wounded, up to two-thirds were hit by the three to five minutes of gunfire the bodyguards fired into the crowd, one official said.
"A large number of people - and quite probably a majority - were killed and wounded as a result of gunfire after the blast," said the second official, a U.N. employee. The official said one internal report is highly critical of the bodyguards' reaction.
Among the dead were 61 students and five teachers, said Education Ministry adviser Hamid Almi. Six members of parliament and five bodyguards also died. The deadliest previous suicide bombing in Afghanistan was in June, when 35 people were killed in a bomb attack on a police bus.
Among the parliamentarians killed was Sayed Mustafa Kazimi, the chief spokesman of Afghanistan's only opposition group, the National Front. No group has claimed responsibility for the attack, and Afghan officials say they don't know who was behind the bombing. The Taliban has denied it was responsible. A government investigation is also under way.
Sayed Mohammad Bakir Hashimi, a Shiite cleric who performed a religious ceremony on Kazimi after the blast, told the AP the lawmaker had three bullet wounds. However, Kazimi's family now denies he was hit by bullets.
Interior Ministry spokesman Zemeri Bashary said most of the victims were hit by ball bearings from the bomb, and not bullets. Bashary gave different casualty numbers than the Education Ministry, saying 59 people in total were killed and 100 wounded.
"There was small number of people injured by bullets," Bashary said. "Bodyguards of lawmakers opened fire into the air and hit some people."
Adrian Edwards, the spokesman for the U.N. mission in Afghanistan, said there is "very, very conflicting" information on the number of gunfire victims.
"The reports we're hearing are that significant numbers were victims of gunfire, but defining who died from gunfire, who died from the explosion is pretty difficult," Edwards said.
Hundreds of children had crowded onto the tree-lined driveway leading to the New Baghlan Sugar Factory to greet visiting lawmakers when the blast went off. Witnesses and survivors describe bodyguards firing into the thick black smoke for up to five minutes after the attack.
"One guy pointed his gun at me, but I put my hands up and said, 'Don't shoot!"' 13-year-old Nezamuddin said this week from his hospital bed. He said a bullet had passed through his ankle, which was bandaged with gauze. "A lot of bullets were fired. ... My friends were hit by bullets."
The trees near the blast are pockmarked from the impact of bomb's ball bearings, and a nearby wall is scarred with bullet holes. Mourners set up a small memorial, including a red plastic flower wreath from the British Embassy. Visitors lit candles on the site, leaving puddles of white wax around the tree.
Dr. Khalil Narmgui, director of the Baghlani-jadid hospital, said his staff treated 11 gunfire victims - five killed and six wounded.
In the nearby city of Pul-i-Khumri, Dr. Mohammad Yousuf Fayyez of the provincial hospital said his staff were not able to differentiate between gunfire and bomb wounds, while Dr. Habib Rahman Fazli said none of those treated at the Pul-i-Khumri Textile Hospital suffered from gunfire.
However, the U.N. official who asked not to be identified said that doctors told investigators that "we know how to differentiate between the bullet and blast wounds, we know how to tell the difference."
One doctor who helped treat patients said he was pressured to hide the truth. "One of the deputies of the ministry - I won't say which ministry - said please don't reveal the high number of casualties by the bullets," the doctor said. He asked not to be named out of fear of reprisals.
The head of Baghlan's elected provincial council said he found it hard to believe that so few people admitted to the hospital were gunfire victims.
"The people said it was raining bullets from the gunmen and security guards," said Sarajuddin, who goes by one name. "It is surprising a mine or suicide bomb could hurt 200 people," he said.
At the Baghlani-jadid hospital this week, six boys and one man lay in a room, recovering from wounds. Ahmad Fareed pulled up his left pant leg to show where surgeons removed a bullet lodged in his left knee. A doctor held up the silver-colored, inch-long bullet.
Outside on the hospital steps sat Mohammad Gul, who buried his 5-year-old son, Nazir. His older son Nassir, 13, is recovering from shrapnel that ripped through his legs.
"Nassir doesn't know about his younger brother. He asked me just now, 'Where is my brother?' ... I told him, 'He's fine. He's at home,"' Gul, 55, said, his voice cracking. "Half of Nazir's head was blown off, and he was hit in the shoulder by a bullet."
Afghanistan's north has been relatively quiet compared with the violence-plagued south, but a handful of attacks, including at least five suicide bombs in neighboring Kunduz province, indicate some anti-government presence here. This was the first suicide bombing in Baghlan province, officials said.
Security officials and elders in Baghlan suspect that the Taliban or militant group Hezb-i-Islami - both of which still have supporters in the area - are behind the attack, although the Taliban denied involvement.
"We have no al Qaeda here. Just Hezb-i-Islami and Taliban," an intelligence official said on condition of anonymity because he was not authorized to speak to the media.
Baghlan police chief Gen. Abdul Rahman Syed Kheil said five suspects have been arrested, but he would not say if the suspects belong to a militant group.
"No faction has claimed responsibility yet," Syed Kheil said, though he believes the attack is "definitely" linked to violence in Kunduz. "There is a network, and they are organizing."