Karzai stopped short of directly blaming neighboring Pakistan, a regional power seen as critical to U.S. efforts to stabilize Afghanistan before NATO combat troops leave by the end of 2014.
On Thursday, a suicide bomber posing as a peace messenger wounded Afghanistan's intelligence chief, Asadullah Khalid, dealing a blow to a nascent reconciliation process. The bomb was hidden in the attacker's underwear, said Karzai.
"Of course we will be seeking clarification from Pakistan because we know this man who came in the name of a guest to meet Asadullah Khalid came from Pakistan. We know that for a fact," said Karzai.
"We will be firmly and clearly seeking clarification and asking for any information that they may have."
Pakistan's government said it would assist in any investigation, but urged Karzai to provide evidence before making such statements.
"Before leveling charges, the Afghan government would do well if they shared information or evidence with the government of Pakistan that they might have with regard to the cowardly attack on (Khalid)," said a spokesman for Pakistan's foreign ministry.
"They would also do well by ordering an investigation into any lapses in the security arrangements around (Khalid)."