The U.S. has dropped its largest non-nuclear bomb in Afghanistan on Thursday, the U.S. military said, in an attack targeting an ISIS tunnel complex in the province of Nangarhar.

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According to the statement, this was the first combat use of the bomb, also known as the "Massive Ordnance Air Blast," or the "Mother of All Bombs."

The number of casualties was not immediately clear and the U.S. military told CNN it was assessing the damage.

Open gallery view The MOAB - Massive Ordnance Air Blast, or Mother Of All Bombs Credit: Wikimedia commons

Open gallery view Achin district, Nangarhar province, Afghanistan

Archive footage: Testing the MOAB

According to CNN reporter David Wright, the bomb targeted ISIS' tunnels and personnel in Nangarhar's Achin district. He added that the bomb was dropped by an MC-130 aircraft, operated by the Air Force Special Operations Command.

>> What is MOAB, 'Mother of All Bombs,' and what is it capable of >>

The bomb blast was also felt in Wall Street, where the Dow Jones industrial average fell 100 points and the S&P 500 fell 0.45 percent. Nasdaq fell 0.23 percent.

The U.S. Forces-Afghanistan Headquarters said in a statement that the strike was "designed to minimize the risk to Afghan and U.S. Forces conducting clearing operations in the area while maximizing the destruction of ISIS-K fighters and facilities," using an abbreviation for Islamic State Khurazan, the militant group's offshoot in Afghanistan.

"This is the right munition to reduce these obstacles and maintain the momentum of our offensive against ISIS-K," General John W. Nicholson, commander of U.S. Forces-Afghanistan, was cited in the statement as saying.

Trump called the bombing "another very, very successful mission" on Thursday and said in response to a question on the authorization of the attack that the military had "total authorization."

"We have the greatest military in the world and they’ve done a job as usual. We have given them total authorization and that’s what they’re doing and frankly that’s why they’ve been so successful lately," Trump told reporters.

>> 'Mother of All Bombs' is Trump's Mother of All Messages >>

White House spokesman Sean Spicer opened his daily news briefing speaking about the use of the bomb and said, "We targeted a system of tunnels and caves that ISIS fighters used to move around freely, making it easier for them to target U.S. military advisers and Afghan forces in the area."

Last week, a U.S. soldier was killed in the same district as the bomb was dropped while conducting operations against ISIS.

"The United States takes the fight against ISIS very seriously and in order to defeat the group, we must deny them operational space, which we did," Spicer said.

He said the bomb was used at around 7 P.M. local time and described the device as "a large, powerful and accurately delivered weapon." The United States took "all precautions necessary to prevent civilian casualties and collateral damage," he said.

The security situation in Afghanistan remains precarious, with a number of militant groups trying to claim territory more than 15 years after the U.S. invasion which toppled the Taliban government.

U.S. officials say intelligence suggests ISIS is based overwhelmingly in Nangarhar and neighboring Kunar province, but estimates of its strength in Afghanistan vary. U.S. officials have said they believe the movement has only 700 fighters but Afghan officials estimate it has about 1,500.

ISIS' offshoot in Afghanistan is suspected of carrying out several attacks on minority Shi'ite Muslim targets.

The Afghan Taliban, which is trying to overthrow the U.S.-backed government in Kabul, are fiercely opposed to ISIS and the two group have clashed as they seek to expand territory and influence.