In an exclusive interview with Al Jazeera's UpFront aired on Friday, Karzai said the US government had allowed ISIL, also known as ISIS, to flourish inside Afghanistan.
"In my view under the full presence, surveillance, military, political, intelligence, Daesh [ISIL] has emerged," he said.
"And for two years the Afghan people came, cried loud about their suffering, of violations. Nothing was done."
Karzai said the US administration of President Donald Trump used ISIL as an excuse to drop a massive bomb on Afghanistan in April 2017.
"And the next day, Daesh takes the next district in Afghanistan," he said referring to the Arabic name of the armed group.
"That proves to us that there is a hand in it and that hand can be no one else but them [the US] in Afghanistan."
GBU-43, the largest non-nuclear bomb, the US used in combat was dropped in the Achin district of Nangarhar province, close to the border with Pakistan, reportedly killing at least 36 ISIL fighters and destroying tunnel complex of the armed group.
The US Central Command (CENTCOM) said the attack was designed to minimise the risk to Afghan and US forces conducting clearing operations in the area.
The explosive, also known as the "mother of all bombs" (MOAB), was equal to 11 tonnes of TNT with a blast radius of 1.6km.
Witnesses said they felt the ground shake after the explosion, while others described towering flames in the aftermath.
At that time, Karzai also condemned the attack as "inhuman and most brutal misuse" of Afghanistan as "testing ground for new and dangerous weapons".
'Potential war crimes'
Karzai also said he welcomed a recent call by the International Criminal Court (ICC) prosecutor to investigate war crimes in Afghanistan, including those committed during his tenure in office.
"She's right to launch such an investigation," Karzai told UpFront host Mehdi Hasan, referring to ICC Chief Prosecutor Fatou Bensouda's request to launch an investigation in Afghanistan.
Karzai also acknowledged that there were human rights violations during his government, and possibly on his watch.
"Definitely, there were violations by the Afghan security forces, by the US, and by others."
Karzai said he would help with any investigation, even into his own potential complicity.
"I have been asking for this so that they come to Afghanistan and investigate as to what has happened in this country."
During the interview, Karzai was also asked to respond to claims by human rights groups that he was warned while in office that human-rights abuses were taking place.
"They are wrong," he said. "They didn't tell me. I told them."
"I told the Western human rights bodies as to what was going on in Afghanistan. They were hiding it. The Western press was hiding it. I told them. I raised it."