The statement issued Sunday also threatened a "complete halt" to negotiations to end the war if Washington continues its attacks.
Vice President JD Vance has postponed his trip.
Pres. Trump said he signed an agreement with Iran that U.S. officials say calls for Tehran to dilute its stockpile of highly enriched uranium and waive sanctions on the country, immediately allowing Iran to sell its oil freely in a major concession from Washington.
Leaders at the G7 summit threw their support behind President Trump's tentative agreement with Iran to open the Strait of Hormuz and further extend a shaky ceasefire.
U.S. allies at the G7 summit worked Tuesday to push the war in Ukraine back up the agenda of President Trump after more than four years of fighting sparked by Russia's full-scale invasion.