Kabul, Afghanistan - An attack that saw the United States drop the largest non-nuclear bomb on Afghanistan was a "brutal act" against Afghan people, the environment and the country's sovereignty, Hamid Karzai, former president, has told Al Jazeera.

The 9,797kg GBU-43 Massive Ordnance Air Blast (MOAB) was unleashed in combat for the first time on Thursday, targeting a complex of caves and tunnels used by ISIL fighters in Nangarhar province, according to the US army.

Dubbed the "Mother of All Bombs", the device can devastate the area around its landing of a radius of more than 1.6km.

"This was an inhuman act, a brutal act against an innocent country, against innocent people, against our land, against our sovereignty, against our soil and against our future," Karzai said in Kabul.

"A bomb of that magnitude has consequences for the environment, for our lives, for our plants, for our water, for our soil - this is poison."

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At least 90 ISIL fighters were killed in the attack, according to the US and Afghan armies.

For the most part, Afghan officials welcomed the bombing, saying it was a step towards security. They have also said that there were no civilian casualties.

But Karzai, who was president from 2004 until 2014, said the US should stop using Afghanistan as a "testing ground" and re-engage with Afghans towards a peaceful solution.

If these conditions are met, he said, "they [US] can stay on - if the Afghan people agree to it. If they continue this militant approach, this heavy-handed military approach in Afghanistan, then, of course, I want them out of the country."

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The massive bomb was dropped after fighting intensified over the past week and US-backed ground forces struggled to advance in the area.

A US soldier was killed on April 8 in Nangarhar while conducting operations against ISIL, which stands for Islamic State of Iraq and the Levant, and is also known as ISIS.

Karzai said he was speaking up because many Afghan officials - some of whom were part of his own cabinet - had endorsed the bombing.

"I considered it a treason and I stood up against them, and I will continue," he said.

"This poison will be there for years and years to come. How can we allow our country to be used this way And why? How many [ISIL fighters] have they killed, 100, 200, 300?

"Why should Afghanistan suffer in such a massive way with a bomb so big, so dangerous that they themselves call it the 'mother of all bombs'.

Karzai's time in office was at times plagued by accusations from the US of corruption and incompetence.

Fahim Dashty, a journalist, politician and political analyst, said that Karzai's comments were unlikely to be welcomed by the majority of Afghans, dismissing the former president's rhetoric as an attempt at "heroism".

"There were lots of problems while he was president of Afghanistan," Dashty told Al Jazeera from Kabul.

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"At least for a decade, he was using US bodyguards to protect himself. Now he is talking about pushing the US to leave Afghanistan. This is something people will not believe."

On the bombing, Dashty said Afghans had little reason not to welcome the attack on ISIL targets.

"There weren't any reports of civilian casualties in the last attack," he said.

"It was said that it was targeting ISIL leaders. As much as it targets terrorist groups, I think people will welcome it."