WASHINGTON - US President Donald Trump on Monday threatened to attack Iran again if Teheran attempts to rearm.

"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 told reporters while welcoming Israeli Prime Minister Benjamin Netanyahu in Florida.

"We'll knock them down. We'll knock the hell out of them," adding that making a "deal" is "much smarter" for Iran.

READ MORE: Israel says killed Iran's military chief in strike on Teheran

Earlier this month, NBC News reported that during their Monday talks, Netanyahu would seek to convince Trump that "Iran's expansion of its ballistic missile program poses a threat that could necessitate swift action."

Iranian Foreign Ministry spokesman Esmaeil Baghaei said last week that Iran's missile program has been developed to defend the country's sovereignty and is "non-negotiable."

READ MORE: Israel vows ‘appropriate response’ if Iran attacks its territory

On June 13, Israel launched surprise airstrikes on several areas in Iran, including nuclear and military sites, killing senior commanders, nuclear scientists, and civilians. On June 22, US forces bombed the three Iranian nuclear facilities of Natanz, Fordow and Isfahan.