Obama renews commitment to Gulf allies after Riyadh visit

At the close of the summit, Obama pledged to remain vigilant against Iran's "destabilising activities" across the Middle East, in an attempt to allay the concerns of Gulf monarchs over Washington's ties with their regional arch-rival after sanctions were lifted earlier this year as part of a US-led landmark deal.

"Even with the nuclear deal we recognise collectively that we continue to have serious concerns about Iranian behaviour," Obama said.

He made reference to Iran's "destabilising activities" in the region but said "none of our nations have an interest in conflict with Iran."

Iran's emergence from international isolation following the nuclear deal has worried the Gulf monarchies, which fear Tehran will be emboldened to seek a still bigger regional role.

Saudi Arabia and its Gulf neighbours accuse Iran of widespread interference throughout the region, where they support opposite sides in the conflicts in Yemen and Syria.

But the US president affirmed that Washington and the monarchies of the Gulf were united in their commitment to improve security in the Middle East.

"Given the ongoing threats in the region, the US will continue to increase our security cooperation with our GCC partners," he added, "Including helping them improve their own capacity to defend themselves."

Saudi Arabia and other Gulf states belong to the US-led coalition that has been carrying out air strikes against IS in Syria and Iraq since mid-2014.

"We remain united in our fight to destroy [IS]," Obama said in Riyadh at the close of the summit.

Washington hopes that in both Syria and Yemen - where a Saudi-led coalition launched air strikes against Iran-backed rebels in March last year - an end to broader fighting can lead to a greater focus on the battle against IS and other militants.

The diplomatic offensive followed months of rising tensions between the US and Saudi Arabia, which have for decades enjoyed strong security ties.

UN-backed peace negotiations between Yemen's warring sides started in Kuwait on Thursday, and Obama "urged all parties" to abide by a ceasefire that began on April 11.

Militants, including the local branch of al-Qaeda, have exploited the Yemen conflict to strengthen their presence in the country's south.

Both Defence Secretary Ashton Carter and US Secretary of State John Kerry joined Obama in Riyadh, holding meetings with top officials.

Yesteryear's relations over

The diplomatic offensive followed months of rising tensions between the US and Saudi Arabia, which have for decades enjoyed strong security ties.

In an interview with CNN, prince Turki al-Faisal, Saudi Arabia's former intelligence chief questioned the future of the relations between Washington and Riyadh, saying they have now irrevocably changed.

The senior royal said that Obama's conduct and declarations has made Riyadh realise the relationship has changed.

"My personal view is that America has changed," he said.

Obama said talk of strains 'was always overblown'

Saudi Arabia will have to "recalibrate" things such as "How far we can go with our dependence on America? How much can we rely on steadfastness from American leadership?" Faisal said.

"And I don't think that we should expect any new president in America to go back to, as I said, the yesteryear days when things were different," he added.

In a highly unusual move, Saudi state news channel Al-Ekhbaria did not broadcast either the start of the summit meeting or Obama's airport arrival on Wednesday.

At a news conference after the summit, Obama said talk of strains "was always overblown", saying there were "tactical" differences on how to deal with Iran.

Obama also told the summit that Washington and Gulf states would work together to lessen the impact of the dramatic fall in oil prices since early 2014.

The US and GCC "will launch a new high-level economic dialogue with a focus on adjusting to lower oil prices, increasing our economic ties and supporting GCC reforms", Obama said.

Saudi Arabia, the world's biggest oil exporter, and its petroleum-rich neighbours have been forced to cut subsidies and adopt other measures to deal with deficits caused by plunging oil prices, which make up the bulk of their revenues.

Agencies contributed to this report.