KABUL — US forces in Afghanistan had not assessed the impact Friday of a massive strike on Islamic State militants in the eastern part of the country, a military spokesman said, raising questions about the already controversial decision to deploy a 22,000-pound bomb on the battlefield.

The Afghan Defense Ministry said three dozen fighters were killed in the attack, which used one of the largest nonnuclear bombs in the US arsenal, the GBU-43, against a network of tunnels and bunkers.

A Pentagon spokesman said its forces would not release an official statement on potential damage or casualties incurred from the strike Thursday night.

It was unclear why the Afghan government released casualty figures but US 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 Captain Bill Salvin, spokesman for US 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, General John W. Nicholson Jr., commander of US 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 US and Afghan forces.

US 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. US 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 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 jihadists across the border.