The former head of U.S. Central Command warned Sunday that the Islamic terror group ISIS has a "strong desire" to attack the U.S. and other foreign powers, a threat he suspects is growing.

Retired Gen. Frank McKenzie told ABC News' "This Week" that U.S. officials should "believe them when they say that."

"I think the threat is growing," McKenzie said, noting threats from ISIS-K after the group took responsibility for a deadly attack in Moscow, Russia, last month that killed more than 140 people. The terror group also claimed responsibility for a mass bombing in Iran in January.

"It began to grow as soon as we left Afghanistan, it took pressure off ISIS-K," McKenzie said, referring to the chaotic U.S. withdrawal from the country in 2021. "So I think we should expect further attempts of this nature against the United States as well as our partners and other nations abroad. I think this is inevitable."

POLISH LEADER WARNS OF 'PREWAR ERA,'URGES EUROPEAN NATIONS TO INVEST IN DEFENSE

McKenzie, who commanded U.S. forces in the Middle East, including the withdrawal from Afghanistan, said the U.S. holds a large enough military presence in Iraq and Syria to combat extremists in the region.

The retired general maintains that the U.S. should have kept a small troop presence in Afghanistan amid the exit instead of completely pulling out and ending the longest war in U.S. history.

President Biden previously claimed there would be an "over-the-horizon capability" to "act quickly and decisively" in Afghanistan, even with troops no longer stationed in the region.

McKenzie said the U.S. now has "almost no ability to see into that country and almost no ability to strike into that country," which he says benefits ISIS and other terror groups.

"If you can keep pressure on them ... in their homeland and their base, it makes it hard for them to conduct these types of attacks," he said. "Unfortunately, we no longer place that pressure on them, so they're free to gain strength, they're free to plan, they're free to coordinate."

McKenzie said he believes "things would be different" and "we might actually be safer than we are" if the U.S. and its allies kept a small presence in Afghanistan, prolonging military involvement in the region.

The deadly attack in Moscow on March 22 highlights the threat of terror groups being able to regroup and plan large-scale operations, McKenzie said.

Despite the dangers, these efforts by the terror groups are more easily detectable, McKenzie said. The U.S. said it alerted the Kremlin to a possible terror plot weeks before that attack happened.

SWEDEN'S DEFENSE MINISTRY WARNING TO BRACE FOR 'WAR' SENDS PUBLIC INTO PANIC

"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 suspects in the Moscow attack opened fire in one of the largest shopping and entertainment complexes in Russia before a fire broke out in the complex, according to the Russian Foreign Security Service.

A U.S. counter-terrorism official told the New York Post that ISIS-K terrorists could cross through the U.S. borders and carry out an attack similar to the one in Moscow. The official said ISIS is growing "bolder" and that its members may attempt to take advantage of the chaos at the southern border and seek out a "bigger" target.

"An attack on US soil is definitely a possibility," the official said. "It would certainly send a message."

McKenzie's comments on Sunday also come after European leaders warned about the prospect of war.

Polish Prime Minister Donald Tusk called on European nations to step up investment in their defense, arguing that the continent is not ready for the current "prewar era."

"I don't want to scare anyone, but war is no longer a concept from the past," he said in a recent interview with European newspapers before pointing to Russia's invasion of Ukraine. "It’s real, and it started over two years ago."

And in January, Swedish defense officials warned about potential war as the nation was close to joining NATO, which has officially happened.

"For a nation for whom peace has been a pleasant companion for almost 210 years, the idea that it is an immovable constant is conveniently close at hand," Swedish Civil Defense Minister Carl-Oskar Bohlin said at the time at Folk och Försvars, or "Society and Defense," annual national conference in Sälen.

"But taking comfort in this conclusion has become more dangerous than it has been for a very long time," he said. "Many have said it before me, but let me do so in an official capacity, more plainly and with naked clarity: There could be war in Sweden."