Just days before the U.S. announced it had dropped the “mother of all bombs” in Nangarhar province east of Afghanistan, ISIS official media bragged about “killing and injuring American soldiers” in the same area.

A massive GBU-43 bomb, the largest non-nuclear bomb ever used in combat, was dropped from an MC-130 aircraft on caves and bunkers said to be housing ISIS fighters in the Achin district of Nangarhar, close to the border with Pakistan, Pentagon said on Thursday.

The terror group’s weekly propaganda magazine, al-Naba, claimed that last Saturday, 11 ISIS fighters carried out an attack against a joint convoy of U.S and Afghan forces in Achin. “Several American crusader soldiers were killed and injured in the attack, alongside 20 Afghan soldiers who were killed,” it wrote.

The New York Times reported that one US soldier had been killed by militants at that time in the region, the first such American casualty in Afghanistan this year.

“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,” White House Spokesman Sean Spicer told reporters on Thursday.

Following the attack, ISIS supporters took the group’s forums and Telegram channel, to boast. “The deployment of the MOAB indicates a degree of desperation in the fight against the Islamic State in Achin district,” one wrote.

Another adherent warned his fellows that “The enemy crossed another line of barbarism” and called on his “brothers and specifically those who are besieged inside Mosul to take all the precautions and prepare for all the possibilities.”

ISIS’ so-called Khorasan Province is based overwhelmingly in Nangarhar and neighboring Kunar. It was formed by former leaders of the Pakistani Taliban and Afghan Taliban fighters who pledged allegiance to ISIS leader Abu Baker al-Baghdadi in the late of 2014 and formed the ISIS’ official branch in Afghanistan and Pakistan area.

The MOAB is a 21,600 pound GPS-guided munition, that was first tested in March 2003, just days before the start of the Iraq war.