US Secretary of State Marco Rubio said Friday he had made progress with allies in opposing Iranian threats to start "tolling" vessels that pass through the strategic Strait of Hormuz.

Iran has partially closed the strait, through which one-fifth of the world's oil normally transits, in retaliation for US-Israeli strikes launched a month ago.

Rubio, after attending talks of the Group of Seven powers, said he had voiced concern that Iran may impose a permanent tolling system "immediately after" the war ends.

"Not only is this illegal, it's unacceptable, it's dangerous to the world, and it's important that the world have a plan to confront it," Rubio told reporters in Paris.

He said he had found "a lot of buy-in" to opposing any Iranian tolling in the strait.

"What we've said is that the countries that are most impacted by that (should) be willing to do something about it, and we'll help them," Rubio said.

"We're willing to be a part of that coalition, but we've encouraged others to sort of put it together," he said.

Rubio said that Britain in particular has "played a prominent role" in bringing together the plan to oppose Iranian tolling.

The Strait of Hormuz was open to international shipping before the US-Israeli attack sparked the war in the Middle East, leading to a surge in global energy prices.