North Atlantic Treaty Organisation commander in Afghanistan, US General John W Nicholson, said "it was the right time to use it tactically against the right target on the battlefield".
Mr Shinwary had earlier confirmed to the BBC that Afghan special forces, with the help of American air support, had begun anti-IS operations in the area two weeks ago.
The number of so-called Islamic State militants killed after USA forces dropped the military's largest non-nuclear bomb on a target in Afghanistan has risen to 94.
In Kabul, Navy Capt. Bill Salvin, spokesman for USA forces, said: "We are still conducting our assessment, and at this time have no evidence of civilian casualties as a result of the GBU-43 drop".
The statement could not be independently verified, and on Friday Afghan and foreign troops in the vicinity were not allowing reporters or locals to approach the scene of the attack.
But Nangarhar Province spokesman Attaullah Khogyani said 90 IS fighters had died, while Achin district governor Esmail Shinwari said "at least 92 Daesh (another name for IS) fighters were killed in the bombing".
Mr Spicer said the United States "takes the fight against Isis very seriously" and said the military took "all precautions necessary to prevent civilian casualties and collateral damage as a result of the operation".
Following the attack, US President Donald Trump said that it was a successful job and that he was very proud of his military.
NBA playoffs set to begin Saturday
Be proactive - Use the "Flag as Inappropriate" link at the upper right corner of each comment to let us know of abusive posts . Whatever Westbrook does, however, he makes many jaws drop in the crowd; the Thunder just do not reflect his excellence.
The Afghan defence ministry said the bomb struck a village area in the Momand valley where IS fighters were using a 300m-long network of caves.
Earlier Friday, the Afghan Defense Ministry, based on initial findings, said that 36 IS militants were killed by the attack.
"We were all scared, and my children and my wife were crying".
Also on Saturday, Khogyani said a district leader and three others were wounded when their vehicle was targeted by a bomb.
The GBU-43 is a GPS-guided munition that had never before been used in combat since its first test in 2003, when it produced a mushroom cloud visible from 32 kilometres away.
The bomb, known officially as a GBU-43B, or massive ordnance air blast weapon (MOAB), unleashes 11 tonnes of explosives.
Meanwhile, former Afghanistan president Hamid Karzai was among the first to condemn the bombing.
Comments