Karzai said Saturday the bomber came from Pakistan and the bombing was planned there, Khaama Press reported. He did not suggest the Pakistani government was involved.
Asadullah Khalid was severely injured Friday when the bomber detonated explosives hidden in his underwear.
The man got in to see Khalid by claiming to be a Taliban peace emissary.
"The job was carried out very professionally and there are bigger and professional hands involved behind the incident since the Taliban group is unable to do that," Karzai said. "We are hoping to receive a positive information from Pakistan and serious cooperation of Pakistan in this regard since this is a very important issue for us."
The main force of the bomb was directed downward by its placement, which may have saved Khalid's life, investigators said.