Secretary of State John Kerry met with Gulf Arab officials to ease their concerns about the warming U.S.-Iran relationship.

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

Kerry and Saudi Foreign Minister Adel al-Jubeir presented a united front when they spoke at a news conference after a meeting of foreign ministers from the Gulf Cooperation Council. The Gulf states have sided with the kingdom in its spat with Iran and backed the rebels fighting to overthrow Syrian President Bashar Assad, a key ally of the Islamic Republic.

Kerry and al-Jubeir said the U.S. and the GCC agreed on the need to confront destabilizing Iranian activities in the region and on an unspecified “understanding” that will allow the U.N.-led Syria negotiations to begin this week.

Al-Jubeir denounced Iran for its “hostile and aggressive stance” against Arab nations. But he said he did not believe that Washington would act rashly in dealing with Tehran because of the nuclear deal just put in place. It has given Tehran access to billions in formerly frozen assets. “Overall, the United States is very aware of the mischief that Iran’s nefarious activities can do in the region,” he said.

Riyadh and Tehran have said the mutual animosity will not affect the Syria talks. But there are serious disagreements over who can represent the opposition at the negotiations, which were supposed to begin Monday but are likely to be delayed for several days.