RIYADH: US Secretary of State John Kerry met with Gulf Arab officials on Saturday to ease their concerns about warming US-Iranian ties and seek consensus on which Syrian opposition groups should be represented at upcoming peace talks.

Kerry held talks in Riyadh with foreign ministers from the Gulf Cooperation Council who have sided with Saudi Arabia in its spat with Iran and who back the rebels fighting to overthrow Syrian President Bashar Assad, a key Iranian ally.

The five nations are concerned about the security ramifications of the Iran nuclear deal, which was implemented earlier this month and has given Tehran access to billions in formerly frozen assets. Kerry was also to meet with Saudi King Salman, the deputy crown prince and foreign minister, as well as the chief negotiator for the Saudi-backed Syrian opposition.

U.S. officials say Washington supports Saudi Arabia in its feud with Iran but would like to see tensions eased to prevent further regional destabilization and complications in the U.N.-led Syrian peace process that is supposed to begin next week in Geneva.

Shiite-led Iran and Sunni-ruled Saudi Arabia are longtime regional rivals who support opposite sides in the wars in Syria and Yemen. Relations plunged to a new low when Saudi Arabia executed a prominent Shiite opposition cleric earlier this month, drawing outrage from Shiites across the region and igniting mob attacks on Saudi diplomatic missions in Iran.

Saudi Arabia and some of its allies responded to those attacks by cutting diplomatic ties with Tehran, and accusing Tehran of being behind numerous terrorist attacks around the world over the past three decades.

Although both Riyadh and Tehran have said the mutual animosity won't affect the Syria talks, there are still serious disagreements over who can represent the opposition at the negotiations, which were initially supposed to begin on Monday but are likely to be delayed for several days.

In Switzerland, before leaving for Saudi Arabia, Kerry said the rivalry remained a concern.

He said that despite implementation of the Iran nuclear deal, the US remained deeply troubled about destabilizing Iranian actions in the region. He said he would renew America's commitment to the security of its Arab friends in the Middle East while he was in Riyadh.

"There is no sudden transformation in these other concerns," he said of Iran. "They exist and we will continue to be vigilant and engaged about them. And that is part of what I'm going to Saudi Arabia about: to make sure our friends see clearly how we will go forward on, together, to address those kinds of concerns."

Kerry said he hoped Syria could become a focal point for improving relations, as all counties have an interest in defeating the Islamic State group and the al-Qaida-affiliated Nusra Front.

"There is something that does bring them closer in terms of Syria, and that is called Daesh," he said, using the Arabic acronym for the Islamic State group. "Both want to kill Daesh. They both want Daesh and Nusra terminated as threats."

Kerry is in Saudi Arabia on the second leg of his latest round-the-world diplomatic mission, which began in Switzerland and will also take him to Laos, Cambodia and China.