The Gulf Cooperation Council (GCC) summit in Riyadh came amid mounting international concern over the Saudi-led air war on Shiite rebels in Yemen, the threat from jihadists and Gulf worries over their Shiite rival Iran.
In a clear reference to Iran, the Saudi monarch spoke of the need to confront an external threat that "aims to expand control and impose its hegemony", threatening regional stability and creating "sectarian sedition".
Hollande, the first Western leader to attend a GCC summit, said France shares the dangers facing the region and he had come "to affirm the commitment of France to be by your side".
All but Oman are in the Saudi-led Sunni coalition that on March 26 launched air strikes in Yemen against Iran-backed Huthi rebels and their allies who seized large parts of the country including Sanaa.
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Yemeni President Abedrabbo Mansour Hadi fled to Riyadh when the rebels advanced on his southern refuge Aden.
Concern has mounted over the air campaign, which has continued despite the coalition announcing late last month it was moving on to a new phase.
The United Nations says at least 1,200 people have been killed in Yemen since March 19, and has repeatedly warned that the already impoverished Arabian Peninsula state faces a major humanitarian crisis.
Hollande told the summit France supports coalition efforts "to ensure the stability of Yemen".
His visit comes as Paris strengthens its political and economic relations with the oil- and gas-rich Gulf monarchies.
He arrived in Riyadh from GCC member Qatar after attending the signing of a 6.3-billion-euro (USD 7-billion) deal between French aerospace firm Dassault and Qatari defence officials.