President Donald Trump threatened to "knock the hell" out of Iran during an appearance with Israeli Prime Minister Benjamin Netanyahu where he expressed concerns about the country rebuilding its capabilities after being targeted by Israeli and U.S. forces over the summer.

"Now I hear that Iran is trying to build up again," Trump said. "And if they are we're going to have to knock them down."

"We'll knock the hell out of them," Trump added. "But hopefully that's not happening."

Netanyahu arrived at Trump's Mar-a-Lago resort Dec. 29 for a meeting in which the leaders were expected to discuss Iran’s ballistic missile program, which has been a concern for Israel. Israel fought a 12-day war against Iran earlier this year that included attacks on ballistic missile sites, and Trump ordered a U.S. military strike on Iranian nuclear sites in June.

This is a developing story that will be updated.

Contributing: Reuters