The head of the U.N.'s nuclear agency signaled Wednesday that Iranian nuclear enrichment sites would be visited by his inspectors, a key component in the interim deal between the United States and Iran to reach an end to the war.

The comment by International Atomic Energy Agency head Rafael Mariano Grossi was the firmest yet from the United Nations agency, which is viewed as key in determining the status of Iran's nuclear stockpile.

The U.S. and Iran offered contradictory remarks Tuesday about whether those sites would be inspected.

"I can understand political statements, they are part of the reality, but the fundamental thing I would like to remind you (of) and draw your attention to is that there has been a Memorandum of Understanding, signed by both presidents," Grossi told journalists at a news conference from the tsunami-hit Fukushima Daiichi nuclear power plant in Japan.

The accord "explicitly states that the nuclear activities that are going to be carried out with the regards of the nuclear material facilities will be supervised by the IAEA — in all letters," he said.

Grossi added: "Obviously, to do that, we have to inspect. Whether this happens the day after tomorrow or in one week or in ten days, it's important, but not essential. This is going to happen."

Those inspections are key for the deal, which calls for Iran's stockpile of uranium to be "downblended" from highly enriched levels.

Rubio arrived in the United Arab Emirates on Tuesday and was scheduled to hold closed-door talks with its leader, Sheikh Mohamed bin Zayed, before flying to Kuwait and then Bahrain, where he will attend a Gulf Cooperation Council meeting.

Rubio said he intended to discuss the US-Iran memorandum of understanding with gulf leaders, which does not address Iran's missile programme and proxies.

He insisted that no country is allowed to impose tolls on the Strait of Hormuz after Oman and Iran, which border the waterway, said they were considering charging "costs" for navigating the key exit route for oil and gas.

"It's an international waterway," he said as he arrived in Abu Dhabi, repeating a position the US has stated throughout the war.

"No country is allowed to charge tolls or fees on an international waterway. That's existing international law."

The Senate on Tuesday approved a House-passed war powers resolution on Iran, marking the first time such a measure has made it through both chambers and signifying a rare rebuke of President Trump's handling of the conflict.

In a 50 to 48 vote, four Republicans — Sens. Susan Collins of Maine, Bill Cassidy of Louisiana, Lisa Murkowski of Alaska and Rand Paul of Kentucky — joined the bulk of Senate Democrats in support of the measure. One Democrat, Sen. John Fetterman of Pennsylvania, opposed. Two Republicans — Mitch McConnell and Dave McCormick — did not vote.

The resolution directs the president to "remove United States Armed Forces from hostilities against the Islamic Republic of Iran," unless Congress declares war or authorizes the use of military force. But the measure is a concurrent resolution, which doesn't carry the force of law and doesn't require the president's signature, meaning it is largely symbolic.

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President Trump said early Wednesday that consumers are being "gouged" because gas prices haven't been falling as fast as crude oil prices have on world markets — so he's told the Department of Justice to begin an investigation.

He said on his Truth Social platform that, "The big Oil Companies are not dropping their price at the pump commensurate with the sharply lower prices they are paying for Oil. Those prices are dropping like a rock! In other words, customers are being 'gouged.' I have instructed the DOJ to immediately start looking into this. Gasoline prices better start going down a lot faster than what I'm seeing!"

Oil prices increased sharply when the Iran war began and gas prices followed. But while crude prices have dropped significantly since an interim agreement was reached to end the fighting, the decline in gas prices hasn't been as rapid. Gas prices generally tend to dip more slowly than they rise with respect to oil costs.