Trump vows to 'knock the hell out of' Iran if nuclear program is rebuilt again after high-stakes meeting

"Now I hear that Iran is trying to build up again, and if they are, we're going to have to knock them down," Trump said. "We'll knock the hell out of them." He added that Iran would be "much smarter" to pursue a deal.

Pressed on whether he would support further Israeli military action if Iran continues advancing its missile or nuclear programs, Trump responded affirmatively. "If they continue with the missiles - yes," he said. "The nuclear - absolutely."

Asked whether he would support the overthrow of Iran's regime, Trump rejected the idea while pointing to unrest inside the country.

The remarks followed a report Sunday by Iran International alleging that Iran's Islamic Revolutionary Guard Corps is accelerating work on unconventional missile payloads, including chemical and biological options, citing unnamed military and security sources.

"The fact that Tehran's ballistic missiles can carry unconventional payloads is not new," said Behnam Taleblu, a senior fellow at the Foundation for Defense of Democracies.

Taleblu pointed to Iran's recent military behavior. 

He added that Iran's history heightens concern, citing Tehran's past use of chemical agents during the Iran-Iraq War in the 1980s and its transfer of such weapons to Libya.