The Afghan Defense Ministry said three dozen fighters were killed in the attack, which used one of the largest non-nuclear bombs in the U.S. arsenal, the GBU-43, against a network of tunnels and bunkers in the east.
A Pentagon spokesman said its forces would not release an official statement on potential damage or casualties incurred from the strike, which was carried out in the Achin district of Nangahar province Thursday night.
It was unclear why the Afghan government released casualty figures but U.S. forces did not. For its part, the Islamic State-linked Amaq News Agency denied that the bombing caused casualties among the militants, according to the SITE Intelligence Group, which monitors online postings from extremist groups and others. The Islamic State offered no evidence to support its claim.
In Kabul, Navy Capt. Bill Salvin, spokesman for U.S. 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."
Also Friday, Gen. John W. Nicholson Jr., commander of U.S. forces in Afghanistan, defended the strike as "the right weapon against the right target," and said it "achieved its intended purpose," which was to remove the tunnel complex as an obstacle to U.S. and Afghan forces on the battlefield.
U.S. and Afghan troops went on the offensive against the local Islamic State branch in March, even as they continue to battle a Taliban insurgency in the rest of the country. U.S. and Afghan officials have said their goal is to "eliminate" the Islamic State from Afghanistan this year, but the Trump administration has not yet said if it plans to commit more troops to the fight. After 16 years of war, the United States and NATO have struggled with how to wind down the conflict here.
But the Islamic State affiliate, which is based in Nangahar, emerged only recently, in the wake of the group declaring a caliphate in Iraq and Syria in 2014. Since then, it has staged deadly attacks on Afghan civilians, particularly in Kabul, but has largely failed to break out of its stronghold in the east. There, the group uses the proximity to Pakistan, which is also plagued by militancy, to build up weapons stockpiles and connect with other jihadists across the border. According to Nicholson, the group, known as Khorasan Province, is made up mostly of Pakistani and Uzbek militants, along with some Afghan fighters who defected from the Taliban.
In Achin and other nearby districts, the Islamic State has terrorized residents, beheading tribal elders, assassinating security officials and closing schools. Even local Taliban commanders fought with the group.
Many of the district's roughly 100,000 residents had already fled, leaving few civilians in the area where the strike took place. No civilians were reported killed, according to U.S. and Afghan officials. Still, some residents and those in neighboring districts described widespread damage and hearing the blast miles away.
"It was a powerful bomb; we felt it several kilometers away," said Khair Mohammad Safi, police chief of the Achin district where the strike took place. Safi, who operates from a neighboring district for security reasons, said he could see flames from the explosion.
"The wave caused by [the blast] was strong. There was a huge fire," he said. "This was the [Islamic State's] main stronghold. They were annihilated. We needed such a bomb for this place."
But just this month, U.S. forces announced that they had nearly decimated the group, claiming to have reduced Islamic State-controlled territory in Afghanistan by two-thirds. The military also said it had killed about half of Khorasan Province's fighters, and carried out hundreds of airstrikes on the group's positions this year alone.
Last week, Army Staff Sgt. Mark R. De Alencar, 37, was killed in Achin by small-arms fire during a combat operation.
"The use of drones turned out to be very effective against Daesh" in Nangahar, said Aryan Youn, a lawmaker from the province, using an Arabic acronym for the Islamic State. "If that was the case, why did the United States want to use such a sophisticated and powerful bomb?"
Local residents, she said, are worried about the impact of the explosion on their health and farmland. Achin is a heavily agricultural district, where farmers grow wheat, cotton and, intermittently, the poppy crop that is used to make opium.
In a statement Friday, the Taliban also condemned the strike, which it called a "show" by U.S. forces who want to convince the world they are taking a strong stance against the Islamic State.
The United States had "no justification" for using such a powerful bomb during combat, said the statement, which was distributed on the instant messaging app Viber.
Taliban fighters have been engaged in a years-long insurgency against the government and international forces in Afghanistan.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)