Morell: Brussels attack also highlights threat to U.S.

European nations have boosted security in the aftermath of a series of explosions that rocked the Belgian capital of Brussels Tuesday morning.

Major U.S. cities, including New York and Washington D.C., have also ramped up security measures, increasing police presence in airports, metro stations and other high-profile locations.

CBS News spoke to several U.S. officials who said there are no credible threats here at this time, but former CIA Deputy Director Michael Morell asserts there is a real "need to worry" that terrorists could bring over similar attacks to the U.S.

"What they mean is no specific, credible threat but ISIS wants to bring that same attack capability that they built in Europe ... to the U.S.," Morell said on "CBS This Morning" Tuesday. "We don't have a good understanding of where they are in that. We need more information on that."

According to Morell, the Brussels bombings - which he believes were accelerated by last week's arrest of Paris attacker Salah Abdeslam - is indicative of the fact that the terror group's "large and sophisticated terrorist network in Europe" has "not been degraded."

The first two explosions at the airport struck a packed departure lounge; another struck at a Maelbeek Metro station in central Brussels about 30 minutes later. Morell said these target locations were a "reflection" of the fact that the terrorists study and adjust to our security protocols.

"So when they look at an airport, they see it's very difficult to get weapons, explosives beyond the security checkpoint ... and one of the ways they adjust to that is, set off your explosives, do your attacks before the security checkpoint," Morell explained.

As Belgium remains at its highest threat level, Morell also urges other European nations and the U.S. to be on high alert for copycat, lone wolf attacks.

Morell also expressed concern for what he called the "worst-case scenario," given the terror group's access to bomb manufacturers in Europe and their capability to produce chemical weapons.

"Bring those two things together, a chemical weapons manufacturing capability in Europe and an attack in Europe using chemical weapons - I worry about that a lot," Morell said.