Speaking at a meeting of Gulf Arab foreign ministers and officials in Bahrain, Rubio said Washington was seeking an enduring peace with long-time foe Iran that would not undermine the security and prosperity of its allies in the oil-rich region, which fear the accord is too soft on Iran after it attacked them in the war.
Iran fought two of the world's most powerful armies - the US and Israel - during the conflict and took effective control of the vital Strait of Hormuz, heavily disrupting oil flows and rattling global energy markets and the wider economy.
"The reality of it is that no country on Earth has the right to charge for the use of international waterways.
And that will never be an acceptable condition of any deal. The president's been fundamentally clear about that," Rubio said on Thursday.
Bahrain Foreign Minister Abdullatif bin Rashid Al Zayani, who chaired the gathering, welcomed Oman's announcement of a corridor for the safe passage of vessels through the strait.
Oman told the meeting that future arrangements for the Strait of Hormuz would not involve transit tolls.
Rubio's three-day tour of the Gulf is the first high-level diplomatic mission since the US-Iran framework agreement to end the conflict, which started on February 28 with US-Israeli strikes on Iran.
He has acknowledged the delicacy of his mission as he seeks to win over Gulf Arab leaders wary that excessive concessions could strengthen Tehran and reshape the region's security balance and oil flows.
At his previous stops in the UAE and Kuwait, Rubio sought to assure officials that the proposed deal was not overly favourable to Iran, which struck several Gulf states during the war.
"We're not going to do anything that undermines the security of our allies, our longstanding allies in the region," he told reporters in Kuwait.
US President Donald Trump said on Tuesday that Iran had agreed to nuclear inspections into "infinity," while Tehran said it had made no such concession in negotiations, raising questions about the viability of their fragile peace deal.
The draft US-Iran agreement includes no limits on Iran's ballistic missiles, a proposed $US300 billion ($A434 billion) reconstruction fund and provisions that could expand Tehran's regional influence and control over critical oil shipping lanes.
Rubio has said he would not ask regional allies to contribute to any reconstruction fund during the trip, even as the accord with Iran suggests that countries in the region would at least be partially responsible for footing the bill.
Some US Gulf allies are privately feeling disappointed over the interim deal that could open the door to US normalisation with Iran, a predominantly Shi'ite country that most Sunni-led GCC states consider their main adversary.
