On Friday he met Saudi King Salman and Crown Prince Mohammed bin Salman, the de facto ruler who US intelligence agencies assess "approved" the 2018 operation that killed journalist Jamal Khashoggi.

After a fist bump with Prince Mohammed, Biden said he raised the Khashoggi case and warned against future attacks on dissidents.

Prince Mohammed chaired the opening session of Saturday's summit, which King Salman did not attend.

He has denied any role in the death of Khashoggi, who was dismembered in the kingdom's Istanbul consulate and whose remains have never been found.

In his remarks on Saturday, Biden told the assembled Arab leaders that "the future will be won by countries that unleash the full potential of their populations... where citizens can question and criticise leaders without fear of reprisal".

Russia's invasion of Ukraine has exposed a once unthinkable divergence between Washington and key Middle East allies Saudi Arabia and the United Arab Emirates, the oil giants that are increasingly independent on the international stage.

The wealthy Gulf nations, which host US forces and have dependably backed Washington for decades, have notably refrained from supporting the Biden administration as it tries to choke Moscow's lifelines, from energy to diplomacy.

Analysts say the new position reveals a turning point in Gulf relations with the US, long the region's protector against neighbour Iran.