A U.S. soldier arrives to the scene where a suicide car bomber attacked a NATO convoy in Kabul, Afghanistan, May 16, 2013 (AP)
KABUL, Afghanistan (CBS NEWS) -- A suicide car bomber attacked a NATO convoy in the Afghan capital on Thursday, killing two troops and four civilian contractors, the international military coalition confirmed. Eight Afghans civilians also died in the explosion and more than 30 were wounded, according to a senior Afghan police official.
The International Assistance Force - Afghanistan (ISAF) did not confirm the nationalities of the slain troops or contractors in its brief written statement, as is customary until families can be notified.
Muslim militant group Hizb-e-Islami claimed responsibility for the early morning attack. The powerful explosion rattled buildings on the other side of Kabul and sent a pillar of white smoke into the sky in the city's east.
An Afghan Army officer and Afghan police at the scene told CBS News' Mukhtar Ahmad that U.S. nationals had been killed in the blast, but the claims could not be immediately confirmed by CBS News, and various sources offered conflicting information on the casualties.
When Ahmad reached the scene of the explosion, approximately one hour after the blast, it was already being secured by a heavy U.S. troop presence, and a team of U.S. military incident investigators arrived soon after.
Kabul provincial police spokesman Hashmad Stanakzi said the suicide bomber attacked the convoy with a car packed with explosives. "The explosion was very big. It set the nearby buildings on fire," Stanakzi said.
Kabul police chief of investigations Zahir Zahir told CBS News that eight Afghan civilians were killed in the explosion, including two children. Many of the wounded were also apparently children. Ahamd says the blast happened at a time of the morning when many local children would have been on the streets on their way to school.
Zahir was not able to confirm any foreign deaths.
Two Kabul hospitals reported that at least 37 wounded were brought in from the scene, city hospitals chief Kabir Amiri said, adding that the toll could increase as more hospitals report in.
The bodies were too badly charred to immediately identify, he added.
A spokesman for Hizb-e-Islami, Haroon Zarghoon, told The Associated Press that one of the movement's operatives carried out the attack on what he described as two vehicles of American advisers. He claimed that most of the American advisers were killed and their vehicles destroyed, though neither Afghan nor coalition officials have confirmed any foreign casualties. Afghan insurgents often exaggerate the success of their attacks.
Hizb-e-Islami is headed by 65-year-old former warlord Gubuddin Hekmatyar, a former Afghan prime minister and one-time U.S. ally who is now listed as a terrorist by Washington. The militia has thousands of fighters and followers across the country's north and east.
Thursday's attack was the second in eight months claimed by Hizb-e-Islami. In September, the militant group claimed responsibility for a suicide car bombing that killed least 12 people. At the time, Hizb-e-Islami said the attack was revenge for the film "Innocence of Muslims," which was made by an Egyptian-born American citizen and infuriated Muslims abroad for its negative depiction of the Prophet Muhammad.
Hizb-e-Islami had been involved last year in seeking to participate in a so-far fruitless peace and reconciliation efforts led by Afghan President Hamid Karzai. Its more moderate parts are thought to have close ties to the Karzai administration.