The former head of U.S. Central Command claims that ISIS wants to attack the United States and the threat is growing.

Retired Gen. Frank McKenzie issued the warning in an interview with ABC News.

They're going to try to do it," McKenzie said on "This Week" on Sunday. "I think the threat is growing."

He noted that an Islamic State affiliate called ISIS-K took responsibility for the Moscow concert hall shooting that left more than 130 people dead and scores more injured. ISIS has a "strong desire" to attack the U.S. and its allies, McKenzie said.

"It began to grow as soon as we left Afghanistan, it took pressure off ISIS-K. So I think we should expect further attempts of this nature against the United States as well as our partners and other nations abroad," McKenzie told news anchor Martha Raddatz. "I think this is inevitable." 

McKenzie argues that the United States should have kept a small military force in Afghanistan.

He noted that ISIS has also claimed responsibility for a January bombing in Iran that killed 84 people and injured at least 284.

He claimed the March 22 terror attack in Russia shows the dangers of militants being able to plan large-scale attacks.

The U.S. said it alerted Russia to warning signs of the attack but was ignored.

"I think there was probably good opportunity for the Russians to have averted this attack had they actually listened to the material that was presented to them," McKenzie said.

The attackers have been identified as citizens of Tajikistan, a former Soviet land that borders Afghanistan. It has seen a growth in Islamic militarism since it became independent.