The Taliban -- usually quick to take responsibility for suicide attacks in the south and east of the country -- has not only denied involvement but also has condemned the November 6 bombing in Baghlan Province.
The details of the attack remain unclear, including a final death toll. But there are fears that violence could escalate and widen rifts between rival factional militia groups in the north.
"We are investigating this whole incident -- unfortunate incident," Afghan President Hamid Karzai told journalists today. "We will take account of all the factors in it. And then we will let you know. A team has already gone for forensic studies of the scene, and another team will go to investigate fully."
Afghans today began three days of national mourning for those killed by the blast. In addition to the six lawmakers, the explosion also killed tribal elders and many schoolchildren.
The blast has once again shaken public confidence in the ability of the Afghan government and some 50,000 foreign troops in the country to provide security.
Many Afghans have told RFE/RL's Radio Free Afghanistan that they see the attack -- initially reported as a suicide bombing -- as an assassination targeting Sayed Mustafa Kazemi, an influential opposition lawmaker and a former commerce minister.
Kazemi was heading a group of lawmakers from parliament's National Economic Committee on a visit to a new sugar factory in Baghlan when he and the other victims were killed by the bomb.
Kazemi was one of the highest-ranking ethnic Hazara and Shi'ite members of the Afghan parliament. He also was the spokesman for the United Afghan National Front -- an opposition political group that was formed last year by northern Afghan militia commanders who had once fought together against the Taliban regime.
Jean MacKenzie, the Kabul-based Afghanistan country director of the Institute for War and Peace Reporting (IWPR), says it was unusual for a Shi'a to be such a strong figure of unity in Afghanistan.
"This is bad news for the north, which has been quite peaceable and where development has been going on at quite a rapid pace," MacKenzie says. "It is also very bad news for the central government."
"There is a lot of mistrust around the versions [of the story] coming out about this," MacKenzie says. "People in Kabul are talking about conspiracies. They are talking about plots to assassinate Kazemi, who was in opposition to the government. Other people are talking about Hizb-e Islami. But at this point, there is a very high level of distrust and tension throughout the country about the possible ramifications of this."
Baghlan Province is a stronghold for illegal armed militia fighters from Hizb-e Islami -- an Islamist mujahedin movement headed by the renegade warlord and former Afghan prime minister, Gulbuddin Hekmatyar.
NATO and UN officials say they have received numerous complaints in recent months that militia fighters in the north have been hoarding weapons to avoid UN-backed disarmament programs.
"Jane's Foreign Report" -- a publication of the London-based Jane's Defense Group -- says Hekmatyar recently has taken a leading role in spreading antigovernment and anti-Western sentiments in northern Afghanistan.
Currently thought to be hiding in the mountainous northeastern regions of Afghanistan that border Pakistan, Hekmatyar reportedly has been sending messages to influential commanders in northern Afghanistan -- inviting them to join him in battle against Western forces.
But parliamentarian Amin Wiqad, a former deputy chairman of Hizb-e Islami and a member of Kazemi's opposition United Afghan National Front, told RFE/RL that he rules out the possibility of a Hizb-e Islami militant carrying out a suicide attack. He says that's because suicide attacks are against the group's ideology.
But Najia Iamaq, a member of parliament from Baghlan Province, told RFE/RL's Radio Free Afghanistan today that she had repeatedly complained to Afghanistan's central government about the growing security threat posed by armed local militia fighters:
"Security has been getting worse and worse every day," Iamaq said. "We, as witnesses, have complained several times and raised the security issue with government officials. Residents of Baghlan, tribal leaders, and elders have been complaining all the time. Unfortunately, the government never seemed to take those complaints seriously."
Meanwhile, an interview conducted by RFE/RL's Radio Free Afghanistan with Safia Siddiqi, a female member of parliament from Nangarhar Province, has fueled further speculation in Afghanistan about the bomb attack.
Siddiqi was meant to be with Kazemi's parliamentary delegation when the explosion occurred. But she says she arrived late at the event because of mechanical problems with her car -- and that she watched from a distance as the lawmakers entered the sugar factory and the bomb went off.
Siddiqi also said the explosion sounded like an incoming missile attack rather than a blast caused by a suicide bomber or an improvised explosive device.
(RFE/RL's Radio Free Afghanistan contributed to this report.)