WASHINGTON, D.C. — Secretary of Defense Ashton Carter told Pentagon reporters that threats of future terrorist attacks on U.S. soil issued after the Islamic State (ISIS/ISIL) reportedly claimed responsibility for the attack in Garland, Texas, should be taken “seriously.”

The Pentagon chief, citing ongoing investigations, said that the threats were inspired by ISIS, not directed by the jihadist group.

ISIS reportedly claimed responsibility for Sunday’s terrorist attack outside a Draw Muhammad cartoon contest in Garland, Texas, marking the first time the terrorist group claims to be behind an attack inside the U.S. homeland.

In taking responsibility for the terrorist attack, ISIS reportedly warned, “What is coming will be more grievous and more bitter and you will see from the soldiers of the Caliphate what will harm you, God willing.”

Moreover, a threat signed by Abu Ibrahim Al Ameriki, allegedly on behalf of ISIS, was posted on a file-sharing site, saying:

The attack by the Islamic State in America is only the beginning of our efforts to establish a wiliyah [province] in the heart of our enemy. … We have 71 trained soldiers in 15 different states ready at our word to attack any target we desire. Out of the 71 trained soldiers 23 have signed up for missions like Sunday.

When asked to comment on ISIS purportedly threatening future attacks, Carter said, “I think we have to take it seriously. And I think our law enforcement and our homeland security folks have been saying the same.”

“I think again, our understanding from the investigations that are going on was that these were inspired by ISIL, not directed by ISIL, which is an important distinction,” he added.

“Still, in all, it’s concerning that there are individuals like this who draw their inspiration from ISIL, and finally, it’s yet another reason why the defeat of ISIL is important,” continued the Pentagon chief. “It’s important in Syria, it’s important in Iraq, and it has this larger meaning because of the ability of a movement like this to inspire a certain sort of person.”

The threat by Al Ameriki mentioned that the Draw Muhammad event’s host, Pamela Geller, the president of the anti-jihad group American Freedom Defense Initiative (AFDI), was the intended target of the two jihadists who carried out the attack.

Both attackers were killed by police before they could do major harm.

In the message, Al Ameriki identified five of the 15 states where he said trained ISIS soldiers are operating: Virginia, Maryland, Illinois, California, and Michigan.

Breitbart News spoke with some experts who dismissed the threat as propaganda and fear tactics.

The experts did say, however, that it is likely that there are some trained ISIS operatives inside the U.S., but they added that the Al Ameriki claim of “71 trained soldiers” is not credible.

Some echoed Carter, stating the threats are likely inspired by ISIS.

Follow Edwin Mora on Twitter: @EdwinMora83.