US President Donald Trump has told Israel's Prime Minister, Benjamin Netanyahu, that Iran will never have nuclear weapons.
He suggested the Iranians thought they could "do what they want" since negotiating a nuclear deal with world powers in 2015.
Mr Trump arrived in Israel from Saudi Arabia, where he sought to win Arab states' support for fighting extremism.
He has called for a peace deal between Israel and the Palestinians.
However, he has been vague about what form it should take, saying he prefers to leave it to both sides to decide between them in direct talks.
The two-day visit to Israel forms part of Mr Trump's first foreign trip as US president.
Speaking in Jerusalem, he said Iran had negotiated a "fantastic deal" with his predecessor, Barack Obama, winning "a lifeline and prosperity".
But "instead of saying thank you", the Iranians were backing terrorism, he said. In a speech earlier on Monday, he accused Iran of "deadly funding, training and equipping of terrorists and militias".
"Iran will never have nuclear weapons, that I can tell you," Mr Trump told Mr Netanyahu.
In a deal with world powers in 2015, Iran accepted curbs on its nuclear programme in return for tangible economic benefits, and the White House confirmed last month that the deal was still holding.