Arriving in Abu Dhabi late on Tuesday for a three-day Gulf trip, Rubio is undertaking his first high-level diplomatic mission on the agreement reached last week to end the four-month-old US-Israeli ​war with Iran.

Asked on arrival if he planned to address allies’ disquiet with the accord, Rubio told reporters:

“That most ​certainly will come up in these discussions.”

He said they would also discuss issues not covered ⁠by the memorandum of understanding.

America’s top diplomat has been largely absent from Iran-related discussions in recent weeks, with Vice President ​JD Vance instead leading a round of talks with Iranian counterparts over the weekend in Switzerland.

Rubio’s remarks during his swing through the region ​will be closely scrutinised to see how the man once known as a hawkish critic of Iran frames a deal that many congressional Republicans argue amounts to capitulation.

Rubio and Vance, both former US senators, are widely viewed within Republican Party circles as potential candidates to succeed Trump, with party ​insiders and early polling often casting the race as a two-way contest between them.

Rubio’s mission is delicate: While he needs to ​defend a preliminary accord that Trump firmly supports, he also has to credibly address the concerns of his Gulf counterparts, who are more ‌circumspect about ⁠the deal.

While Gulf leaders pushed for peace during the four-month-long conflict, many were surprised and disappointed by the terms of the accord.

US regional allies are especially concerned that Iran could use the proposed $300 billion reconstruction fund to rebuild its military.

The accord also does not address Tehran’s ballistic missile capacity, a concern for Gulf states, all of which were struck by Iranian missiles and ​drones in the war.

Tehran has ​noted that the Gulf states ⁠made various logistical accommodations for Washington’s war effort, while hosting US military bases that were central to the conflict.

Among the countries Rubio is visiting are the United Arab Emirates and Kuwait.

​Both nations host strategic US military bases, and both were hit by an onslaught of ​Iranian missiles, resulting ⁠in civilian deaths.

The UAE faces particularly severe economic strains, as the war caused thousands of expatriates at the core of its non-oil economy to flee, provoking questions about the long-term viability of an expanding global financial centre so close to a country that attacked it.

Last ⁠week, Reuters reported ​that Iran set up secretive new cells in Iraq to carry out ​attacks on Gulf countries, including Kuwait and the UAE.

Those cells carried out at least seven drone attacks against sites in Kuwait, the UAE and Saudi ​Arabia during a roughly one-month period in April and May, Reuters reported.