"From Lebanon to Iraq to Yemen, Iran funds, arms and trains terrorists, militias and other extremist groups that spread destruction and chaos across the region," Trump said in a major speech in Saudi Arabia.
"Until the Iranian regime is willing to be a partner for peace, all nations of conscience must work together to isolate it... and pray for the day when the Iranian people have the just and righteous government they so richly deserve."
Trump, visiting the kingdom at the start of his first foreign tour since taking office, told dozens of Muslim leaders invited to Riyadh for a special summit that he brought "a message of friendship and hope and love".
He appealed to Muslim nations to ensure that "terrorists find no sanctuary on their soil" and announced an agreement with Gulf countries to fight financing for extremists.
He said Arab, Muslim and Middle Eastern nations "have born the brunt of the killings and the worst of destruction in this wave of fanatical violence".