Seventeen people died in the attack, including 13 foreigners, most of them Americans, and four Afghans. The attacker rammed his car packed with explosives into the NATO vehicle.
Although the Taliban claimed responsibility, The New York Times reported Afghan and U.S. officials said they suspect the attack was the work of the brutal Haqqani faction whose members seem better trained and organized than other Taliban members.
The Haqqanis, based in Pakistan, have lately been involved in such attacks as if to tell the Afghans and rest of the world they are able to target foreign troops, the Times reported.
One Western diplomat told the Times if the Haqqanis were responsible for the latest attack, it would be in response to U.S. Secretary of State Hillary Clinton who, in her recent visit to Pakistan, pressed on with the demand the government go after the Haqqanis, who have havens in the North Waziristan area.
"No one goes to this much trouble if they don't think you'll get the message," the diplomat told the Times.
Agreeing, Afghan political analyst Haroun Mir said such attacks are planned to respond to the pressure from the United States on Pakistan. Mir said the Pakistanis also are sending a message that they "are not willing to abandon their support of the Taliban."
Brig. Gen. Carsten Jacobson, spokesman for the NATO forces in Afghanistan, told the Times many of the recent high-profile attacks in Kabul had been clearly linked to the Haqqanis.
Afghan intelligence service spokesman Lutfullah Mashal said:"Kabul is their area of operation, and all the signs and indications point to the Haqqani network."