The British monarch highlighted the importance of continued US help for Ukraine in its war with Russia, and the dangers of isolationism.
Both Britain and the United States have maintained over the years that Tehran should not develop nuclear weapons.
Tehran denies seeking them but says it has the right to develop nuclear technology for peaceful purposes, including enrichment, as a party to the Nuclear Non-Proliferation Treaty.
The US and Israel launched a war against Iran on February 28. Tehran responded with strikes on what it described as US interests across the region, many of them in Gulf countries.
A ceasefire was announced on April 8 through Pakistani mediation, followed by talks hosted in Islamabad on April 11-12, but the negotiations ended without an agreement.
Trump later said the truce had been extended at Pakistan’s request pending a proposal from Tehran.