KABUL, Afghanistan — A day after the United States military dropped its most powerful conventional bomb on caves used by Islamic State affiliates in eastern Afghanistan, officials said on Friday that dozens of militants had been killed, but that they were still trying to assess the full extent of the damage. Residents said the blast had been felt tens of miles away.

The strike on Thursday targeted a set of mountain tunnels in the Achin district, a stronghold of the Islamic State’s regional affiliate, and it was the first use in combat of the GBU-43/B Massive Ordnance Air Blast, referred to as the “mother of all bombs.” The bombing was part of an intense air campaign against the Islamic State, with American airstrikes in Afghanistan averaging as many as 10 a day in the first two weeks of April.

Gen. Dawlat Waziri, a spokesman for the Afghan Defense Ministry, said initial information indicated that 36 militants had been killed and three large caves destroyed in the bombing in Nangarhar Province. However, Attaullah Khogyani, a spokesman for the provincial governor’s office, said 82 militants had been killed.

Gen. John W. Nicholson Jr., the commander of American and NATO forces in Afghanistan, said on Friday at a news conference in Kabul, the capital, that the Islamic State was using caves, tunnels and “an extensive belt of improvised explosive devices,” or roadside bombs, to resist Afghan and coalition operations.