The French finance ministry told AFP that around 500 million euros is required but that only just over half has been raised so far. The ministry set a target of spring 2027 to muster the rest of the funds.
A Group of Seven meeting was moved to Paris at the last minute, with only scheduling reasons given for the change. The visit by Rubio will be his first abroad since the US midterm elections.
US media have described Rubio as a potential candidate to succeed Trump. His trip is the first he has made abroad since Republicans lost those elections.
Europeans, however, are eager to see a resolution and a return to normal shipping traffic in the Strait of Hormuz, an energy transit hub.
Washington has kept the option of new strikes open since Republicans lost the midterm elections.
The gathering comes as Russia's war against Ukraine grinds toward its fifth anniversary. Russia launched its full-scale invasion of its neighbor in February 2022.
Washington will take over the G7 presidency from France in 2027.
Asked about widespread protests in France, Rubio said he was not worried. He said he trusted US counterparts on the ground, who advised him that it was safe to attend the G7 meeting. Trump, speaking of the Iranians on Friday, said:"We're dealing with them now.".