Saudi Arabia's King Salman told Gulf monarchs they must stand up to Iran, as he hosted a regional meeting also attended by French President Francois Hollande.
The Gulf Cooperation Council (GCC) summit came amid mounting international concern about the impact on civilians of Saudi-led air strikes targeting Yemeni rebels.
Hollande, the first Western leader to attend a GCC summit, said France shared the dangers facing the region and he had come "to affirm the commitment of France to be by your side."
The summit in the Saudi capital, Riyadh, brought together leaders from Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates.
All but Oman are in the Saudi-led Sunni coalition that on March 26 launched air strikes in Yemen against the Tehran-backed Huthi rebels and their allies who have seized large parts of the country including the capital, Sana'a.
U.S. Secretary of State John Kerry will visit Saudi Arabia this week before security talks in France.