U.S. Secretary of State John Kerry is in Saudi Arabia for talks with Gulf Arab officials on their deteriorating relations with Iran and on the Syria peace process.

Kerry arrived in Riyadh early Saturday from Switzerland, where he said he was going to meet with wary U.S. partners in the Gulf to discuss the way forward with Iran now that the landmark nuclear deal has been implemented. He said he would also continue pressing for consensus on which Syrian opposition groups should be represented at the United Nations-led negotiations, due to start Monday in Geneva.

Shiite-led Iran and Sunni-ruled Gulf Arab states support opposite sides in the Syria conflict and disagree on which Syrian groups should be eligible for the talks. Animosity over Iran's support for Syrian President Bashar Assad has broadened in recent weeks after Saudi Arabia executed a Shiite cleric, prompting an attack on the Saudi embassy in Tehran. Saudi Arabia and some other Arab states then severed diplomatic relations with Iran and have launched campaigns accusing it of being behind numerous terrorist attacks around the world.

The spat had led to fears that the Syrian political transition could be jeopardized, but each country has pledged that its rancor will not affect the negotiations.

A senior State Department official said the U.S. backs its longtime partner Saudi Arabia in the feud but would like to see both Iran and Saudi Arabia put this episode behind them. The official, who spoke on condition of anonymity because he was not authorized to speak publicly to the delicate diplomacy, said there had been no signs yet that Saudi-Iran hostility was compromising the Syria peace effort.

However, there are still serious disagreements over who can represent the opposition at the talks, which diplomats say are likely to be delayed for several days.

Before leaving Switzerland, Kerry said the rivalry remained a concern. He added that despite the implementation of the Iran nuclear deal, the U.S. 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 al-Qaida affiliates like the al-Nusra Front.

"There is something that does bring them closer in terms of Syria, and that is called Daesh," he said, using the Islamic State's Arabic acronym. "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 will also take him to Laos, Cambodia and China.